100 coins

 

 

 

 

 

 

 

Question:

There are 100 coins scattered in a dark room. 10 have tails facing up and 90 are facing heads up.You can’t simply tell which coins are which. How can you arrange the coins into two piles such that contain the same number of tails up coins?

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Solution: The piles don’t need to be the same size to make a pile of 10 coins and a pile of 90 coins. So flip all of the ten coins and it is guaranteed that the piles have the same number of tails.

 

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