Three young brothers had saved $10 each to buy a second hand locomotive. They arrive at the shop and see one on the shelf, Behind the counter is a young girl serving as the owner of the shop, is out. The brothers ask, “How much is that loco on the shelf” she replies “$30” The brothers hand over the $30 they had saved between them and leave the shop with the loco. At the same time, the owner arrives back and seeing that the loco is missing from the shelf, asks the girl how much she had sold it for, she states $30. The owner says, “Oh dear, it was only $25, run after them and give them $5 back”. Out runs the girl with the $5. On nearing the brothers, she has a brainwave, and thinks to herself, “I’ll keep $2 and give the brothers $1 each back.” This she does, but here is the problem. The brothers have now paid only $9 each for the loco, 3*9= $27 plus the $2 in the girls handbag, where has the other $1 gone……………………….