Six weights
A nice variation of the classic balance scale weighing puzzle.
Puzzle
You have six weights. One pair is red, one pair is white, one pair is blue. In each pair, one weight is a trifle heavier than the other, but otherwise appears to be exactly like its mate. The three heavier weights (one of each color) all weigh the same. This is also true of the three lighter weights. In two separate weighings on a balance scale, how can you identify which is the heavier weight of each pair?
See also
References
Problem Solving by Thomas DeFranco and Charles Vinsonhaler.