Basic Computer Knowledge Test Questions and Answers

Probability -Aptitude


A family has two children. find the probability that both the children are girls given that at least one of them is a girl? 

   A.) 1/4
   B.) 2/3
   C.) 1/3
   D.) 1/4

Answer: Option 'C'

Let b stand for boy and g for girl. The sample space of the experiment is 
S = {(g, g), (g, b), (b, g), (b, b)} 
Let E and F denote the following events : 
E : ‘both the children are girls’ 
F : ‘at least one of the child is a girl’ 
Then E = {(g,g)} and F = {(g,g), (g,b), (b,g)} 
Now E n F = {(g,g)} 
Thus P(F) = 3/4
and P (E n F )= 1/4 
Therefore P(E|F) = P(E ∩ F)/P(F) = (1/4)/(3/4) = 1/3

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