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Logic, Sets and Probability

Probability : Worked Examples

Example 1

The table below shows the number of male and female that play a sport in an IB class

Calculate, on randomly selecting a student, the probability of selecting:

1. A female?

2. A male sports player?

3. A sports player given she is female? (this is a conditional probability question) We are only interested in females =

4. Male given he is a sports player? (this is a conditional probability question) We are only interested in the sports players =

Example 2

A bowl of fruit contained 5 oranges and 7 apples a child selected two pieces of fruit to take to school.

1. Draw a tree diagram to show the possible choices made

2. Calculate the probability of selecting an orange?

3. Given an orange was selected, what is the probability that a apple was selected first?

(i)

(ii) There are three ways of getting an orange

(iii) We now need to use the conditional probability formula

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