Brain Teasers & Mental Math
You flip 3 fair coins. Given that at least one is a head, what is the probability all three are heads?
Model answer
1/7.
There are 2³ = 8 equally likely outcomes. Conditioning on 'at least one head' removes only TTT, leaving 7 equally likely outcomes. Exactly one of them (HHH) is all heads → 1/7.
Formally: P(HHH…
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