Chapter 18: Probability (Exercise)

Notes:

1. The probability of an event A occurring is defined as

P (A )= Number of outcomes of event ANumber of outcomes of sample space

=n(A)n(S)

2. 0≤P (A )≤1P(A) = 1, means the event A will definitely occur.P(A) = 0, means the event A will definitely not occur.

3. If A’ is the complement of an event A, then

P (A ' )=1−P(A)4. Probability of an event A OR event B is given by

P (A∪B )=n(A∪B)n(S)

5. Probability of events A and B is given by

P (A ∩B )= n(A∩B)n(S)

6. Probability of two or three independent trees can be used when the event are said to be statistically independent.

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Exercise:

1. A box contains 5 identical cards with a letter written on each. The letters are M, A, E, H and S. A card is drawn at random.

a. Write down the sample space.b. Determine the number of possible outcomes for the following events.

i. P is the event getting a consonant.ii. Q is the event of getting a vowel.

2. A bag contains 3 green marbles, 4 red marbles and 6 blue marbles. A marble is drawn at random from the bag. Find the probability of getting

a. A green marble.b. A marble which is not red.

3. Two dice are rolled together. Find the probability of gettinga. Two numbers less than 4.b. Two numbers with a sum of more than 7.

4. Eleven letters of the word “PROBABILITY” are written on eleven cards. A card is drawn at random. Find the probability that the card drawn is either a “B” or an “I”.

5.

1 2 3 45 6 7 89 10 11 1213 14 15 16

The diagram shows a board with 16 numbered squares of which some are shaded. A dart is thrown at the board. Find the probability that it will hit

a. An even number in a shaded square.b. An odd number or a shaded square.

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Chapter 18: Probability (Exercise)

6. There are 5 red marbles and 10 green marbles in a bag. If a marble is picked at random, find the probability that (i) the marble is red and green. (ii) the marble is red.

7. Aming 1000 students in school, 500 students go to school by bus, 200 students walk to school and 300 students travel by car. If a student is selected at random, find the probability that the selected student

a. Walks or goes by car to school.b. Travels by bus or walks to school.

8. In a dart competition, the probabilities that Ali and Rahmin strike the target are 1/3, and 3/5 respectively. Find the probability that

a. Ali or Rahmin will strike the target.b. Only Rahmin will strike the target.c. Both do not strike the target.

9. A lady attended interviews at companies X and Y. The probabilities that companies X and Y will offer her a job are 3/5 and 4/7 respectively. Find the probability that the lady

a. Fails to get a job in both company X and Y.b. Gets a job in company X.

10. Two dices are rolled together. Find the probability of getting a total score of 10.

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