Originally Posted by nealtw
each bag has . . .one ounce coins
Nineteen bags have fake coins that weigh 1/10th ounce less than the real ones
and each fake bag also has real coins that weigh the full ounce?
Never mind: I would have never come up with the method for finding the good bag.
You need to change more keywords in your statement of the problem to prevent a web search from hitting on this solved problem.