I am a two-digit number. The sum of my digits is 9. If you subtract 45 from me, my digits reverse their order. What number am I?
72
Let the number be 10x + y. x + y = 9. 10x + y - 45 = 10y + x. Simplifying gives 9x - 9y = 45, so x - y = 5. Combining x + y = 9 and x - y = 5 yields x = 7, y = 2.
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: Medium. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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