### 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.

Hide Hint Show Hint Hide Answer Show Answer

## What Next?

View a Similar Brain Teaser...

If you become a registered user you can vote on this brain teaser, keep track of which ones you have seen, and even make your own.

### Solve a Puzzle

Comments hidden to avoid spoilers.

## Follow Braingle!