I am an even, two-digit number. Both of my digits are identical. My digits do not share any factors with 5. What number am I?
44
The even two-digit numbers with identical digits are 22, 44, 66, 88. The digits 2, 6, and 8 share a factor with 5 (their factors include 1 and themselves, wait—5 is prime, numbers sharing a factor with 5 must be multiples of 5, meaning 55. But 55 is odd. Oh, digits sharing a factor with 5 means digits that are 5 or share common divisors with 5. The digit 5 shares a factor with 5. So digits 2, 4, 6, 8 do not share any factors with 5 except 1. Wait, 44 has digit 4. 4 and 5 are coprime. So 44 works.
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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