What single digit, when multiplied by any other single digit, results in a number whose individual digits always sum to that original single digit (or reduce to it)?
9
All positive multiples of 9 have a digital root of 9 (e.g., 9 * 7 = 63, and 6 + 3 = 9).
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Easy. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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