### Brain Teasers

# Two Coins

Probability
Probability puzzles require you to weigh all the possibilities and pick the most likely outcome.

Suppose I flip two coins without letting you see the outcome, and I tell you that at least one of the coins came up heads. What is the probability that the other coin is also heads?

### Hint

You might initially think that the answer is 1/2, but it is not so.### Answer

1/3.For two coins, there are four possible outcomes: HH, HT, TH, and TT. Since we know that at least one was a head, we can eliminate TT. Of the remaining three possibilities, only 1 allows the second head: HH.

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