Brain Teasers & Mental Math
Probability: a family has two children, and you're told at least one is a boy. What is the probability both are boys? (The classic two-child puzzle.)
Model answer
1/3.
Equally likely birth orders for two children: BB, BG, GB, GG. 'At least one boy' eliminates GG, leaving {BB, BG, GB} — three equally likely cases. Only BB has two boys, so the probability is…
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