1. Note 10:Conditional Probability
A/B “A occurs knowing that B has occurred”
Given
P(A /B) = P(A B)
P(B)

2. Example 1: In a school of 88 boys, 32 study Economics, 28 study History and 39 do not study either subject.
Find the probability that a student studies Economics and History
If the student studies Economics find the probability he does not study History

3. E H 11 21 17 39
P(H and E) =
P(H’ /E) = P(H’ E) =
P(E) =

4. Example 2: A packet of seeds contains 40% red seeds and 60% yellow seeds. The probability that a red seed grows is 0.9 and that a yellow seed grows is A seed is chosen at random from the packet.
Given that the seed grows, find the probability that it is red?

5. G R NG G Y NG
P(R/G) = P(R G)
P(G)

6. Studies:
Page 522
Exercise 16I.2