GATE 2014 EC (EC1) – Question 12
Half the families in a housing society have one child each; the remaining half have two each. Find the probability that a child picked at random has a sibling.
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Correct answer: 0.65 to 0.68
Explanation
Take an equal number N of one-child and two-child families. They contain N+2N=3N children, of whom2N belong to two-child families and have a sibling. Sampling children rather than families therefore gives2N/(3N)=**2/3≈0.6667**.