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?
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