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Puzzle of the Day

These puzzles are also printed in Eight days a week, a booklet published by the Association of Teachers of Mathematics.The Association of Teachers of Mathematics

Write any three-digit number whose first digit differs from its last by 1. For instance 627 or 506. Reverse the digits then subtract the smaller from the larger number. Do this with several numbers. What do you notice? Does this always happen?

Answer: always gives 99

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