If you are given many closed sacks filled with different amounts of identical marbles, how could you determine the weight of a single marble without opening the sacks? (Assume the weight of the sack material can be ignored.)
The only thing I could think of was to weigh the bag but its says to ignore the weight.
Look for the greatest common divisor of all bag weights.
http://en.wikipedia.org/wiki/Greatest_common_divisor