II OBM

Question

Box A contains black balls and box B contains white balls. Take a certain number of balls from A and place them in B. Then take the same number of balls from B and place them in A. Is the number of white balls in A then greater, equal to, or less than the number of black balls in B?

Accepted Answer

Suppose we move n balls from A to B, then x white balls from B and n-x black balls from B. That leaves x black balls in B. So both numbers equal x.