This is one of my favorites:
A Supervisor in a Ball-Bearing factory receives a Memo from management saying that one of the 10 machines he manages is messing up, that machine is producing 9g bearings instead of 10g. The problem is that they don't know which machine is messing up.
Management gave him a scale and they allowed him to use it only once!! to figure out the bad machine.
After a few hours of thinking the supervisor found a way to solve the problem.
How did he do it?