Coin Riddle
You are in a totally dark room. In front of you there are an uncountable number of coins. Each coin has a silver and gold side, and due to the darkness, you cant tell which side is which. The exit to this treacherous trap will open once there are 2 piles, each with the same amount of sliver side up coins. You only know that right now, there are 20 silver side up coins in the pile. You are allowed to flip as many coins as you want. How many coins should you take from the overall pile to make your new pile?(Note: you want to take the least amount of coins possible.)
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1 solution
The answer of 20 is really obvious, and this is why. Lets say you take 20, and there are 9 silver side up coins. So now, there are 11 silver side up coins in the old pile. Now, you flip them all over and now the 9 silver side up coins become gold side up coins. However, this also means the other 11 gold side up coins become silver side up. Now the number of silver side up coins are the same on either side. This will work no matter how many silver coins you pick up. (Try this at home with pennies and you will se that it always works if you pick 20.)