I am a prime number between 20 and 40. Subtract 1 from me, and the result is divisible by 6. Add 1 to me, and the result is a multiple of 8. What number am I?
31
The primes between 20 and 40 are 23, 29, 31, and 37. 31 - 1 = 30 (divisible by 6), and 31 + 1 = 32 (a multiple of 8).
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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