I don't have the exact numbers I first saw for this problem. This is how it goes.
Say there are M jelly beans in a jar, and say 5 people guessed 107, 96, 122, 120 and 106. Someone tells you that the numbers are off by 11, 26, 5, 15, and 16 (these numbers probably don't work). You don't know which error goes with which guess. With this size problem we can solve it using trial and error, but how would you solve it in general?