Multiply me by any positive integer, then sum the digits of that product repeatedly until a single digit remains, and you will always end up right back at me. What single-digit number am I?
9
Any positive multiple of 9 has a digital root (repeated sum of digits) equal to 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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