What is the probability that exactly one sibling is affected
3.31 What is the probability that exactly one sibling is affected?
A/ Let
A = &lbrace older child is affected &rbrace,
B = &lbrace younger child is affected &rbrace
|
P(A) = 0.5 |
P = 1- 0.5= 0.5 |
|
P(B) = 0.5 |
P() = 1- 0.5 = 0.5 |
Let P(C1) represents probability that exactly A has affected;
P(C1) = P(A ) = (0.5 × 0.5) = 0.25
P(C2) represents probability that exactly B has affected;
P(C2) = P( B ) = (0.5 × 0.5) = 0.25
Let P(C) represents probability of exactly one sibling is affected, then:
P(C) = P(C1) + P(C2) = 0.25 + 0.25 = 0.5 = 50%
3.32 What is the probability that neither sibling is affected?
A/
Let P(D) represents probability that neither sibling is affected
P(D) = P( ) = (0.5 × 0.5) = 0.25 = 25%
3.33 Suppose the older child is affected. What is the probability that the younger child is affected?
A/
P (B I A) = P (B A) / P (A)
= P (B) * P(A) / P (A)
= 0.5 × 0.5 / 0.5
= .5
= 50%
