You are blindfolded (you can’t see). There are 100 coins lying on a table. 80 are tails-up and 20 are heads-up. You need to divide them into two groups of x and y each (x+y = 100). You can pick any coin and flip it (if its tails, it will become head and if its head, it will become tail), but you can’t see so you don’t know which coin you are flipping. In the end, the two groups should contain equal number of heads. What will be the value of x and y?