Try this one. It is not as simple as it might sound but not as complicated either.

You have six identical balls except two are painted red, two are painted blue and two are painted white. You know one ball of each color weighs 10 pounds and one ball of each color weighs 11 pounds. (So each color has one lighter ball and one heavier ball).

You have a scale and pan balance but no weights. Only the balance and the six balls.

What is the minimum number of weighings you have to do to determine which are the heavier balls and which are the lighter balls?