This is a simple gem I found again in a Martin Gardner book – More Mathematical Puzzles and Diversions, Chapter 14, Puzzle #8. I urge all the adults who try this puzzle to put this as a 2-minute challenge for themselves, children might take more. No algebra please!
An absent minded bank clerk switched the dollars and cents when he cashed a cheque for Mr Brown, giving him dollars instead of cents and cents instead of dollars. After buying a five-cent newspaper, Brown discovered that he had left exactly twice as much as his original cheque. What was the amount of the cheque?
As always, please send your answers directly to me at firstname.lastname@example.org. If you like the puzzle, please share it with others. If you have interesting puzzles to share, please send them to me at my e-mail given above.