(This "nonsense puzzle" gets its name from the puzzle I saw it from)
A shopper went into a shop and wanted a dollar's worth of chestnuts when he gave the shopkeeper a one dollar bill and was given five chestnuts. "It is not enough; I ought to have a sixth," the shopper remarked. "But you will have five too many if I gave you one chestnut more", the shopkeeper replied.
How many chestnuts should the man have gotten for 3 twenty dollar bills?