GATE ECE 2014 Set 1 | Question: 2

Question

In a housing society, half of the families have a single child per family, while the remaining half have two children per family. The probability that a child picked at random, has a sibling is ________.

Answer 1

Let E1 = one children family   

E2 = two children family and   

A = picking a child then by Baye’s theorem, required probability is

P(E2/A) = (1/2x)/(1/2 . x/2 + 1/2 .x) = 2/3 = 0.667

here x is number of families.