Due to popular demand, I've re-phrased this question.
Each of 10 large barrels is filled with golf balls that all look alike.
The balls in nine of the barrels weigh 30,000 mg and the balls in one of the barrels weigh 30,001 mg.
With only one weighing session on a scale that indicates the exact weight -- a digital scale, if you will -- of the mass it is weighing, how can you determine which barrel contains the heavier golf balls?
Hints!
You can do anything you want with the barrels or their contents before weighing them, but you won't be able to tell which one is heavier just by lifting them.
You're not required to weigh a barrel. You can weigh anything, but only once!
This is not a trick question. And yes, the answer involves weighing something on the scale!