Conditional Probability Example1

A family has two children. It is already known that one of them is boy, find the probability that both the children are a boy.


Sample space = {BB, BG, GB, GG}

let's say that A is an event that one of them is boy 

So E(A)= {BB,BG,GB}

      P(A) = 3/4

now let us say B is an event for the second boy for this possible sample space will be 

 S= {BG, GB, BB } we are neglecting  BB because it is already given that there is at least one boy

So P(B/ A)=  1/3