Probability Theory


#1

In a population of N families, 50% of the families have 3 children, 30% of the families have 2 children and the rest have one child. What is the probability that a randomly picked child belongs to a family with 2 children ?

A. 3/23
B. 6/23
C. 3/10
D. 3/5


#2

Let N = 100

Family Type 1) 50 families have 3 children = 50 * 3 = 150 children
Family Type 2) 30 families have 2 children = 30 * 2 = 60 children
Family Type 3) 20 families have 1 children = 20 * 1 = 20 children

Question is simply asking about probability of number of children in “Family Type 2”

= (No of children in Family Type 2) / (Total No. of children)

= 60/230

= 6/23

So option B is correct.