Question

1. Helen has two children. Assume that the probability of each child being a girl is 50%, and is independent with the gender of the other child. Given that at least one of Helen’s children is a girl, what is the probability that the other child is a boy?

   (A) 1/3 (B) 1/2 (C) 2/3 (D) 3/4 (SHOW WORK)

Answer 1

Sample space for 2 kids = {BB, BG, GB, GG}

Probability of girl and a boy, P(G and B) = 2/4

Probability of at least one Girl, P(G) = 3/4

probability that the other child is a boy given that at least one of Helen’s children is a girl, P(B | G) =

= P(G and B) / P(G)

=(2/4) / (3/4)

= 2/3

Answer C.