Probability

IntroductionExamplesKey words

Practice questionsVenn diagrams

A single number is written on each of six pieces of card

One card is selected from the six, the number is recordedand then returned to the set Assuming it is equally likely to pick any card use the results to predict the six numbers

Results:

ProbabilityWith probability we are dealing with the chance of an event

happening (or not happening). An event could be anything from ‘obtaining a head when flipping a coin’ to ‘it raining next Thursday’.

The probability that an event, A, will happen is written as P(A).

The probability that the event A, does not happen is called the complement of A and is written as A'

As either A must or must not happen then:P(A') = 1 – P(A)...as probability of a certainty is equal to 1

ExamplesA box contains the numbers2, 4, 6, 6, 9, 20, 34A number is picked at random from the boxWhat is the probability it is:

(a) Even (b) a multiple of 3 (c) a factor of 18

Probability 1 worksheet

Key words:Sample / possibility spaceOutcomeEqually likely outcomesEventComplement of an eventMutually exclusive eventsAddition LawTrialRelative Frequency

Venn diagramsIn a class of 20 students, 12 study Maths and 13 study English. How many study both subjects?

Results so far

Probability 2 worksheet

Example:When a fair die is rolled find the probability of rolling a 4 or a 1. P(4 or 1) = P(4) + P(1)

= 1/6 + 1/6= 2/6 = 1/3

Handy hint:Exclusive events will involve the words ‘or’, ‘either’ or something

which implies ‘or’.Remember ‘OR’ means ‘add’.

A box contains 5 red beads and 3 blue beads.Two beads are taken out of the bag.• What is the probability of the two beads being

the same colour?• What is the probability of the beads being

different colours?