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Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Math 124: Lecture for Week 6 of 17

David MeredithDepartment of Mathematics

San Francisco State University

March 4, 2008

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

What we will do tonight

1 Review Tests

2 Questions and Answers

3 Probability TheoryBasic Terms and DefinitionsRules for Probability CalculationsConditional Probability

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

What we will do tonight

1 Review Tests

2 Questions and Answers

3 Probability TheoryBasic Terms and DefinitionsRules for Probability CalculationsConditional Probability

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

What we will do tonight

1 Review Tests

2 Questions and Answers

3 Probability TheoryBasic Terms and DefinitionsRules for Probability CalculationsConditional Probability

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Review tests

• Midterm Review• Essay Question• Distribution of Answers

• Midterm

• Quiz www.cmu.edu/oli

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Review tests

• Midterm Review• Essay Question• Distribution of Answers

• Midterm• Quiz www.cmu.edu/oli

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Questions and Answers

Review My Response questions for the week

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

Suppose you want to apply probability theory to somesituation or experiment.

• The set of possible outcomes in your situation is calledthe sample space

• The sample space for tomorrow’s weather is {sunny,cloudy, rainy}

• The sample space for tossing a coin is {H,T}• The sample space for tossing a nickel and a dime is:

Nickel H H T TDime H T H T

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

Suppose you want to apply probability theory to somesituation or experiment.• The set of possible outcomes in your situation is called

the sample space

• The sample space for tomorrow’s weather is {sunny,cloudy, rainy}

• The sample space for tossing a coin is {H,T}• The sample space for tossing a nickel and a dime is:

Nickel H H T TDime H T H T

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

Suppose you want to apply probability theory to somesituation or experiment.• The set of possible outcomes in your situation is called

the sample space• The sample space for tomorrow’s weather is {sunny,

cloudy, rainy}

• The sample space for tossing a coin is {H,T}• The sample space for tossing a nickel and a dime is:

Nickel H H T TDime H T H T

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

Suppose you want to apply probability theory to somesituation or experiment.• The set of possible outcomes in your situation is called

the sample space• The sample space for tomorrow’s weather is {sunny,

cloudy, rainy}• The sample space for tossing a coin is {H,T}

• The sample space for tossing a nickel and a dime is:Nickel H H T TDime H T H T

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

Suppose you want to apply probability theory to somesituation or experiment.• The set of possible outcomes in your situation is called

the sample space• The sample space for tomorrow’s weather is {sunny,

cloudy, rainy}• The sample space for tossing a coin is {H,T}• The sample space for tossing a nickel and a dime is:

Nickel H H T TDime H T H T

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• An event in your situation is a subset of a samplespace

• For tomorrow’s weather, “it doesn’t rain” = {sunny,cloudy} is an event

• For two coins, nickel comes up H is an event• For two coins, one H and one T is an event

• Two special events• the empty subset of the sample space = “nothing

happens”• the whole sample space = “something happens”

• Two events are disjoint if they don’t contain anycommon outcome

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• An event in your situation is a subset of a samplespace

• For tomorrow’s weather, “it doesn’t rain” = {sunny,cloudy} is an event

• For two coins, nickel comes up H is an event• For two coins, one H and one T is an event

• Two special events• the empty subset of the sample space = “nothing

happens”• the whole sample space = “something happens”

• Two events are disjoint if they don’t contain anycommon outcome

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• An event in your situation is a subset of a samplespace

• For tomorrow’s weather, “it doesn’t rain” = {sunny,cloudy} is an event

• For two coins, nickel comes up H is an event

• For two coins, one H and one T is an event• Two special events

• the empty subset of the sample space = “nothinghappens”

• the whole sample space = “something happens”

• Two events are disjoint if they don’t contain anycommon outcome

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• An event in your situation is a subset of a samplespace

• For tomorrow’s weather, “it doesn’t rain” = {sunny,cloudy} is an event

• For two coins, nickel comes up H is an event• For two coins, one H and one T is an event

• Two special events• the empty subset of the sample space = “nothing

happens”• the whole sample space = “something happens”

• Two events are disjoint if they don’t contain anycommon outcome

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• An event in your situation is a subset of a samplespace

• For tomorrow’s weather, “it doesn’t rain” = {sunny,cloudy} is an event

• For two coins, nickel comes up H is an event• For two coins, one H and one T is an event

• Two special events

• the empty subset of the sample space = “nothinghappens”

• the whole sample space = “something happens”

• Two events are disjoint if they don’t contain anycommon outcome

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• An event in your situation is a subset of a samplespace

• For tomorrow’s weather, “it doesn’t rain” = {sunny,cloudy} is an event

• For two coins, nickel comes up H is an event• For two coins, one H and one T is an event

• Two special events• the empty subset of the sample space = “nothing

happens”

• the whole sample space = “something happens”

• Two events are disjoint if they don’t contain anycommon outcome

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• An event in your situation is a subset of a samplespace

• For tomorrow’s weather, “it doesn’t rain” = {sunny,cloudy} is an event

• For two coins, nickel comes up H is an event• For two coins, one H and one T is an event

• Two special events• the empty subset of the sample space = “nothing

happens”• the whole sample space = “something happens”

• Two events are disjoint if they don’t contain anycommon outcome

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• An event in your situation is a subset of a samplespace

• For tomorrow’s weather, “it doesn’t rain” = {sunny,cloudy} is an event

• For two coins, nickel comes up H is an event• For two coins, one H and one T is an event

• Two special events• the empty subset of the sample space = “nothing

happens”• the whole sample space = “something happens”

• Two events are disjoint if they don’t contain anycommon outcome

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

Question 1:

1 Find the sample space associated with drawing arandom card from an ordinary deck of cards.

2 How many outcomes are there?3 Are the events “draw a spade” and “draw a face card”

disjoint?4 Give an example of two disjoint events with at least four

outcomes in each event.

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• In the context of a probability model, every event has aprobability, which is a decimal number between 0 and1.

• If A is an event, a subset of the sample space S, thenthe probability of A is denoted P(A)

• P(∅) = 0The probability that nothing happens is 0

• P(S) = 1The probability that something happens is 1

• If A and B and disjoint events, then

P(A ∪ B) = P(A) + P(B)

The probability that either A or B happens is the sum ofthe probabilities of A and B

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• In the context of a probability model, every event has aprobability, which is a decimal number between 0 and1.

• If A is an event, a subset of the sample space S, thenthe probability of A is denoted P(A)

• P(∅) = 0The probability that nothing happens is 0

• P(S) = 1The probability that something happens is 1

• If A and B and disjoint events, then

P(A ∪ B) = P(A) + P(B)

The probability that either A or B happens is the sum ofthe probabilities of A and B

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• In the context of a probability model, every event has aprobability, which is a decimal number between 0 and1.

• If A is an event, a subset of the sample space S, thenthe probability of A is denoted P(A)

• P(∅) = 0The probability that nothing happens is 0

• P(S) = 1The probability that something happens is 1

• If A and B and disjoint events, then

P(A ∪ B) = P(A) + P(B)

The probability that either A or B happens is the sum ofthe probabilities of A and B

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• In the context of a probability model, every event has aprobability, which is a decimal number between 0 and1.

• If A is an event, a subset of the sample space S, thenthe probability of A is denoted P(A)

• P(∅) = 0The probability that nothing happens is 0

• P(S) = 1The probability that something happens is 1

• If A and B and disjoint events, then

P(A ∪ B) = P(A) + P(B)

The probability that either A or B happens is the sum ofthe probabilities of A and B

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• In the context of a probability model, every event has aprobability, which is a decimal number between 0 and1.

• If A is an event, a subset of the sample space S, thenthe probability of A is denoted P(A)

• P(∅) = 0The probability that nothing happens is 0

• P(S) = 1The probability that something happens is 1

• If A and B and disjoint events, then

P(A ∪ B) = P(A) + P(B)

The probability that either A or B happens is the sum ofthe probabilities of A and B

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine the sample space of an experiment

• In the context of a probability model, every event has aprobability, which is a decimal number between 0 and1.

• If A is an event, a subset of the sample space S, thenthe probability of A is denoted P(A)

• P(∅) = 0The probability that nothing happens is 0

• P(S) = 1The probability that something happens is 1

• If A and B and disjoint events, then

P(A ∪ B) = P(A) + P(B)

The probability that either A or B happens is the sum ofthe probabilities of A and B

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

A consequence of these rules is:

•∑

o∈S P(o) = 1• The sum of the probabilities of all the individual

outcomes is 1• In the special case that there are n equally likely

outcomes, then the probability of each outcome is1n

.

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

A consequence of these rules is:•

∑o∈S P(o) = 1

• The sum of the probabilities of all the individualoutcomes is 1

• In the special case that there are n equally likely

outcomes, then the probability of each outcome is1n

.

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

A consequence of these rules is:•

∑o∈S P(o) = 1

• The sum of the probabilities of all the individualoutcomes is 1

• In the special case that there are n equally likely

outcomes, then the probability of each outcome is1n

.

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

A consequence of these rules is:•

∑o∈S P(o) = 1

• The sum of the probabilities of all the individualoutcomes is 1

• In the special case that there are n equally likely

outcomes, then the probability of each outcome is1n

.

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

Question 2: Assuming that you are equally likely to drawany card, what is the probability of:

1 drawing the ace of spades2 drawing an ace3 drawing a face card4 drawing a spade

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

Question 3: If you toss a nickel and a dime, what is theprobability that you get one H and one T?

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Translate real world problems into probabilistic

representation.

• Math 124.16 consists of

Fr So Jr Sr Uncl Cl Fac TotalF 9 5 4 8 3 1 0 30M 5 5 2 1 2 1 1 17

Total 14 10 6 9 5 2 1 47

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Translate real world problems into probabilistic

representation.

• The situation under consideration is choosing a personat random from our class

• The sample space is the whole class• Each person is an outcome• “Choosing a junior” is an event• “Choosing a senior” is an event• These events are disjoint• “Choosing an upper-division student” is the union of

these events

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Translate real world problems into probabilistic

representation.

• The situation under consideration is choosing a personat random from our class

• The sample space is the whole class

• Each person is an outcome• “Choosing a junior” is an event• “Choosing a senior” is an event• These events are disjoint• “Choosing an upper-division student” is the union of

these events

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Translate real world problems into probabilistic

representation.

• The situation under consideration is choosing a personat random from our class

• The sample space is the whole class• Each person is an outcome

• “Choosing a junior” is an event• “Choosing a senior” is an event• These events are disjoint• “Choosing an upper-division student” is the union of

these events

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Translate real world problems into probabilistic

representation.

• The situation under consideration is choosing a personat random from our class

• The sample space is the whole class• Each person is an outcome• “Choosing a junior” is an event

• “Choosing a senior” is an event• These events are disjoint• “Choosing an upper-division student” is the union of

these events

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Translate real world problems into probabilistic

representation.

• The situation under consideration is choosing a personat random from our class

• The sample space is the whole class• Each person is an outcome• “Choosing a junior” is an event• “Choosing a senior” is an event

• These events are disjoint• “Choosing an upper-division student” is the union of

these events

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Translate real world problems into probabilistic

representation.

• The situation under consideration is choosing a personat random from our class

• The sample space is the whole class• Each person is an outcome• “Choosing a junior” is an event• “Choosing a senior” is an event• These events are disjoint

• “Choosing an upper-division student” is the union ofthese events

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Translate real world problems into probabilistic

representation.

• The situation under consideration is choosing a personat random from our class

• The sample space is the whole class• Each person is an outcome• “Choosing a junior” is an event• “Choosing a senior” is an event• These events are disjoint• “Choosing an upper-division student” is the union of

these events

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

• The probability of choosing any person is the same asthe probability of choosing any other person.

• So the probability of choosing any particular person is1

47= 0.021.

• If we choose somebody• The probability of choosing someone is 1• The probability of choosing nobody is 0

• The probability of choosing a junior is647

= 0.13

• The probability of choosing a senior is9

47= 0.19

• The probability of choosing an upper-division student is0.13 + 0.19 = 0.32

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

• The probability of choosing any person is the same asthe probability of choosing any other person.

• So the probability of choosing any particular person is1

47= 0.021.

• If we choose somebody• The probability of choosing someone is 1• The probability of choosing nobody is 0

• The probability of choosing a junior is647

= 0.13

• The probability of choosing a senior is9

47= 0.19

• The probability of choosing an upper-division student is0.13 + 0.19 = 0.32

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

• The probability of choosing any person is the same asthe probability of choosing any other person.

• So the probability of choosing any particular person is1

47= 0.021.

• If we choose somebody

• The probability of choosing someone is 1• The probability of choosing nobody is 0

• The probability of choosing a junior is647

= 0.13

• The probability of choosing a senior is9

47= 0.19

• The probability of choosing an upper-division student is0.13 + 0.19 = 0.32

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

• The probability of choosing any person is the same asthe probability of choosing any other person.

• So the probability of choosing any particular person is1

47= 0.021.

• If we choose somebody• The probability of choosing someone is 1

• The probability of choosing nobody is 0

• The probability of choosing a junior is647

= 0.13

• The probability of choosing a senior is9

47= 0.19

• The probability of choosing an upper-division student is0.13 + 0.19 = 0.32

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

• The probability of choosing any person is the same asthe probability of choosing any other person.

• So the probability of choosing any particular person is1

47= 0.021.

• If we choose somebody• The probability of choosing someone is 1• The probability of choosing nobody is 0

• The probability of choosing a junior is647

= 0.13

• The probability of choosing a senior is9

47= 0.19

• The probability of choosing an upper-division student is0.13 + 0.19 = 0.32

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

• The probability of choosing any person is the same asthe probability of choosing any other person.

• So the probability of choosing any particular person is1

47= 0.021.

• If we choose somebody• The probability of choosing someone is 1• The probability of choosing nobody is 0

• The probability of choosing a junior is647

= 0.13

• The probability of choosing a senior is9

47= 0.19

• The probability of choosing an upper-division student is0.13 + 0.19 = 0.32

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

• The probability of choosing any person is the same asthe probability of choosing any other person.

• So the probability of choosing any particular person is1

47= 0.021.

• If we choose somebody• The probability of choosing someone is 1• The probability of choosing nobody is 0

• The probability of choosing a junior is647

= 0.13

• The probability of choosing a senior is9

47= 0.19

• The probability of choosing an upper-division student is0.13 + 0.19 = 0.32

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find probability of events in the case when all outcomes are

equally likely.

• The probability of choosing any person is the same asthe probability of choosing any other person.

• So the probability of choosing any particular person is1

47= 0.021.

• If we choose somebody• The probability of choosing someone is 1• The probability of choosing nobody is 0

• The probability of choosing a junior is647

= 0.13

• The probability of choosing a senior is9

47= 0.19

• The probability of choosing an upper-division student is0.13 + 0.19 = 0.32

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

Question 4: What is the probability of choose a malefreshman or a female senior?

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Next we need to develop some rules for calculatingnon-obvious probabilities

• There are two rules.• Master them and you can do any probability problem.

• The rules are based on three little words: “and”, “or”and “not”

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Next we need to develop some rules for calculatingnon-obvious probabilities

• There are two rules.

• Master them and you can do any probability problem.

• The rules are based on three little words: “and”, “or”and “not”

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Next we need to develop some rules for calculatingnon-obvious probabilities

• There are two rules.• Master them and you can do any probability problem.

• The rules are based on three little words: “and”, “or”and “not”

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Next we need to develop some rules for calculatingnon-obvious probabilities

• There are two rules.• Master them and you can do any probability problem.

• The rules are based on three little words: “and”, “or”and “not”

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

The Negation Rule

• If A is an event, then not A is the complement of A, allthe outcomes that aren’t in A.

• If A = choose a junior, thennot A = choose someone who is not a junior

• P(not A) = 1− P(A) because not A and A are disjoint,so

P(A) + P(not A) = P(A ∪ not A)

= P(S)

= 1

• The probability that a student is not a junior is1− 0.13 = 0.87

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

The Negation Rule

• If A is an event, then not A is the complement of A, allthe outcomes that aren’t in A.

• If A = choose a junior, thennot A = choose someone who is not a junior

• P(not A) = 1− P(A) because not A and A are disjoint,so

P(A) + P(not A) = P(A ∪ not A)

= P(S)

= 1

• The probability that a student is not a junior is1− 0.13 = 0.87

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

The Negation Rule

• If A is an event, then not A is the complement of A, allthe outcomes that aren’t in A.

• If A = choose a junior, thennot A = choose someone who is not a junior

• P(not A) = 1− P(A) because not A and A are disjoint,so

P(A) + P(not A) = P(A ∪ not A)

= P(S)

= 1

• The probability that a student is not a junior is1− 0.13 = 0.87

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

The Negation Rule

• If A is an event, then not A is the complement of A, allthe outcomes that aren’t in A.

• If A = choose a junior, thennot A = choose someone who is not a junior

• P(not A) = 1− P(A) because not A and A are disjoint,so

P(A) + P(not A) = P(A ∪ not A)

= P(S)

= 1

• The probability that a student is not a junior is1− 0.13 = 0.87

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

The Negation Rule

• If A is an event, then not A is the complement of A, allthe outcomes that aren’t in A.

• If A = choose a junior, thennot A = choose someone who is not a junior

• P(not A) = 1− P(A) because not A and A are disjoint,so

P(A) + P(not A) = P(A ∪ not A)

= P(S)

= 1

• The probability that a student is not a junior is1− 0.13 = 0.87

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

Question 5: What is the probability that a student is anundergraduate?

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• If A and B are events, then A or B = A ∪ B, all theoutcomes in A or B or both.

• If A = junior and B = male thenA or B = junior or male or both

• A and B = A ∩ B, all the outcomes in A and in B• In the example, A and B = male junior

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• If A and B are events, then A or B = A ∪ B, all theoutcomes in A or B or both.

• If A = junior and B = male thenA or B = junior or male or both

• A and B = A ∩ B, all the outcomes in A and in B• In the example, A and B = male junior

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• If A and B are events, then A or B = A ∪ B, all theoutcomes in A or B or both.

• If A = junior and B = male thenA or B = junior or male or both

• A and B = A ∩ B, all the outcomes in A and in B

• In the example, A and B = male junior

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• If A and B are events, then A or B = A ∪ B, all theoutcomes in A or B or both.

• If A = junior and B = male thenA or B = junior or male or both

• A and B = A ∩ B, all the outcomes in A and in B• In the example, A and B = male junior

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• The Addition Rule

P(A and B) + P(A or B) = P(A) + P(B)

• If you know any three of these probabilities, you canfind the fourth.

• In the example, P(junior) = 0.13, P(male) = 0.36 andP(junior male) = 0.043

• Thus

P(male or junior) = P(male) + P(junior)− P(male and junior)

= 0.36 + 0.13− 0.043= 0.45

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• The Addition Rule

P(A and B) + P(A or B) = P(A) + P(B)

• If you know any three of these probabilities, you canfind the fourth.

• In the example, P(junior) = 0.13, P(male) = 0.36 andP(junior male) = 0.043

• Thus

P(male or junior) = P(male) + P(junior)− P(male and junior)

= 0.36 + 0.13− 0.043= 0.45

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• The Addition Rule

P(A and B) + P(A or B) = P(A) + P(B)

• If you know any three of these probabilities, you canfind the fourth.

• In the example, P(junior) = 0.13, P(male) = 0.36 andP(junior male) = 0.043

• Thus

P(male or junior) = P(male) + P(junior)− P(male and junior)

= 0.36 + 0.13− 0.043= 0.45

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• The Addition Rule

P(A and B) + P(A or B) = P(A) + P(B)

• If you know any three of these probabilities, you canfind the fourth.

• In the example, P(junior) = 0.13, P(male) = 0.36 andP(junior male) = 0.043

• Thus

P(male or junior) = P(male) + P(junior)− P(male and junior)

= 0.36 + 0.13− 0.043= 0.45

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

Question 6: What is the probability that a student is a maleor a senior?

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• The addition rule has one special case that you havealready seen

• A and B are disjoint events if they have no outcomes incommon

• That means A ∩ B = ∅ or P(A and B) = 0.• In that case our general addition rule simplifies to the

rule for disjoint events:

P(A or B) = P(A) + P(B)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• The addition rule has one special case that you havealready seen

• A and B are disjoint events if they have no outcomes incommon

• That means A ∩ B = ∅ or P(A and B) = 0.• In that case our general addition rule simplifies to the

rule for disjoint events:

P(A or B) = P(A) + P(B)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• The addition rule has one special case that you havealready seen

• A and B are disjoint events if they have no outcomes incommon

• That means A ∩ B = ∅ or P(A and B) = 0.

• In that case our general addition rule simplifies to therule for disjoint events:

P(A or B) = P(A) + P(B)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• The addition rule has one special case that you havealready seen

• A and B are disjoint events if they have no outcomes incommon

• That means A ∩ B = ∅ or P(A and B) = 0.• In that case our general addition rule simplifies to the

rule for disjoint events:

P(A or B) = P(A) + P(B)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Example: A = choose a male freshman andB = choose a female senior

• P(A) =547

= 0.11 and P(B) =8

47= 0.17

• A and B are disjoint events

P(A and B)

= P(student is male freshman and a female senior)= 0

P(choose a male freshman or a female senior)= P(A or B)

= P(A) + P(B)

= 0.11 + 0.17= 0.28

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Example: A = choose a male freshman andB = choose a female senior

• P(A) =547

= 0.11 and P(B) =8

47= 0.17

• A and B are disjoint events

P(A and B)

= P(student is male freshman and a female senior)= 0

P(choose a male freshman or a female senior)= P(A or B)

= P(A) + P(B)

= 0.11 + 0.17= 0.28

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Example: A = choose a male freshman andB = choose a female senior

• P(A) =547

= 0.11 and P(B) =8

47= 0.17

• A and B are disjoint events

P(A and B)

= P(student is male freshman and a female senior)= 0

P(choose a male freshman or a female senior)= P(A or B)

= P(A) + P(B)

= 0.11 + 0.17= 0.28

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Example: A = choose a male freshman andB = choose a female senior

• P(A) =547

= 0.11 and P(B) =8

47= 0.17

• A and B are disjoint events

P(A and B)

= P(student is male freshman and a female senior)= 0

P(choose a male freshman or a female senior)= P(A or B)

= P(A) + P(B)

= 0.11 + 0.17= 0.28

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Example: A = choose a male freshman andB = choose a female senior

• P(A) =547

= 0.11 and P(B) =8

47= 0.17

• A and B are disjoint events

P(A and B)

= P(student is male freshman and a female senior)= 0

P(choose a male freshman or a female senior)= P(A or B)

= P(A) + P(B)

= 0.11 + 0.17= 0.28

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

Question 7: If you draw a card at random from an ordinarydeck, what is the probability that you get:

1 a nine or a jack2 a club or a jack

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• We say that A and B are independent events ifP(A and B) = P(A)P(B)

• in that case the occurrence of one of the events doesnot affect the probability that the other will occur.

• Example: If I toss a nickel and a dime, the probabilitythat the nickel comes up H is not affected by how thedime falls.

P(N = H and D = H) = 0.25= 0.5× 0.5= P(N = H)P(D = H)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• We say that A and B are independent events ifP(A and B) = P(A)P(B)

• in that case the occurrence of one of the events doesnot affect the probability that the other will occur.

• Example: If I toss a nickel and a dime, the probabilitythat the nickel comes up H is not affected by how thedime falls.

P(N = H and D = H) = 0.25= 0.5× 0.5= P(N = H)P(D = H)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• We say that A and B are independent events ifP(A and B) = P(A)P(B)

• in that case the occurrence of one of the events doesnot affect the probability that the other will occur.

• Example: If I toss a nickel and a dime, the probabilitythat the nickel comes up H is not affected by how thedime falls.

P(N = H and D = H) = 0.25= 0.5× 0.5= P(N = H)P(D = H)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• We say that A and B are independent events ifP(A and B) = P(A)P(B)

• in that case the occurrence of one of the events doesnot affect the probability that the other will occur.

• Example: If I toss a nickel and a dime, the probabilitythat the nickel comes up H is not affected by how thedime falls.

P(N = H and D = H) = 0.25= 0.5× 0.5= P(N = H)P(D = H)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Example: If choose a card and put it back, the value ofthe card has no effect on the value of the next carddrawn. The probability that I will draw a spade and thena 9 is

P(card 1 = spade) = 0.25P(card 2 = nine) = 0.077

P(card 1 = space and card 2 = nine) = (0.25)(0.077)

= 0.019

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Example: If choose a card and put it back, the value ofthe card has no effect on the value of the next carddrawn. The probability that I will draw a spade and thena 9 is

P(card 1 = spade) = 0.25P(card 2 = nine) = 0.077

P(card 1 = space and card 2 = nine) = (0.25)(0.077)

= 0.019

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

• Example: If choose a card and put it back, the value ofthe card has no effect on the value of the next carddrawn. The probability that I will draw a spade and thena 9 is

P(card 1 = spade) = 0.25P(card 2 = nine) = 0.077

P(card 1 = space and card 2 = nine) = (0.25)(0.077)

= 0.019

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Apply probability rules in order to find the likelihood of an

event

Question 8: If you choose two students at random from ourclass with replacement,

1 what is the probability that you get two women?2 what is the probability that you get a man and a

woman?

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Break

Please return in 15 minutes.

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find conditional probabilities and interpret them

Question 9:1 If you choose a woman from our class, what is the

probability that she would be a junior?2 If you choose a junior from our class, what is the

probability that the person would be a woman?

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find conditional probabilities and interpret them

• If you want to find the probability that somethinghappens, and you already know something about thesituation, we call that a conditional probability—theprobability is conditional on the knowledge

• Example: if you know that the person you chose fromour class was a woman, what would the probability bethat she was a junior?

•4

30= 0.13

• Example: if you know that the person you chose fromour class was a junior, what would the probability bethat the person was a woman?

•46

= 0.67

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find conditional probabilities and interpret them

Question 10:1 If you choose a man from our class, what is the

probability that he would be a senior?2 If you choose someone from our class, what is the

probability that the person would be a male senior?

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find conditional probabilities and interpret them

• The probability that B is true, given that A is true, isdenoted P(B|A)

• P(junior | woman) = 0.13• P(woman | junior) = 0.67

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find conditional probabilities and interpret them

Question 11:1 Find P(man)2 Find P(man and sophomore)3 Find P(sophomore | man)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Explain the reasoning behind conditional probability, and

how this reasoning is expressed by the definition of

conditional probability

• We have seen that P(B|A) =P(B and A)

P(A)

• P(sophomore|man) =P(sophomore and man)

P(man)

• In other words, P(B|A)P(A) = P(B and A)

• P(sophomore|man)P(man) = P(sophomore and man)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Determine whether two events are independent or not

• A and B are independent events ifP(B)P(A) = P(B and A)

• It is always true that P(B|A)P(A) = P(B and A)

• Therefore A and B are independent events ifP(B) = P(B|A)

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find conditional probabilities and interpret them

Question 12:1 Show that the probability of drawing a spade from an

ordinary deck of cards is independent of the probabilityof drawing a face card.

2 If you remove an ace from the deck, what is theprobability that a card drawn at random from theremaining cards is a king?

3 Use the formula

P(card 1 = ace)P(card 2 = king|card 1 = ace)

= P(card 1 = ace and card 2 = king)

to calculate the probability of drawing an ace followedby a king.

Math 124:Week 6

Review Tests

Questions andAnswers

ProbabilityTheoryBasic Terms andDefinitions

Rules for ProbabilityCalculations

ConditionalProbability

Find conditional probabilities and interpret them

Question 13:1 If you selected two people at random from our class,

what is the probability that the first person is a man andthe second person is a woman?

2 If you selected two people at random from our class,what is the probability that one person is a man and theother person is a woman?

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