The Othello, also known as reversi, is played with 64 round chips that are white on one side and black on the other. When you dump the game pieces, 10 of them are left with the white face up and the rest show their black face.
With our eyes closed, we mix the chips without flipping them and they ask us to form two groups of chips so that in both we have the same number of chips with the white face up.
How can we get it without looking at the chips?
To achieve this we must separate a group of 10 chips and turn them all so that those with the white face up will now show the black face and vice versa. In this way, if we have selected X white tokens, these will become black and therefore in the other group we will have 10 - X white tokens.
The rest of the chips we have turned in the group of 10 will be 10 - X white chips that were previously black.