Dark Coin Riddle (SOLUTION)
Although this riddle sounds difficult to solve, the solution is in fact very simple. This is because any pile with N coins facing silver side up means that the remaining coins are facing gold side up, and vice versa.
We know there are initially 20 coins facing up in the pile, but can't remember which.
Take any 20 coins and then flip them each. You have solved the riddle!
Why it works:
If your second pile has N coins facing silver side up, then:
The first pile has 20 - N coins facing silver side up.
Your second pile has 20 - N coins facing gold side up.
Flipping your second pile means it has 20 - N coins facing silver side up.
Thus, the first pile and second pile both have 20 - N coins facing silver side up.
Source:
This riddle was taken from the TED-Ed YouTube channel: https://youtu.be/pnSw8g3DPHw
Check out the puzzle (without the solution) by clicking here!
