My age right now is a multiple of 7. Next year, my age will be a multiple of 5. I am younger than 80. How old am I?
21
Multiples of 7 under 80 where adding 1 yields a multiple of 5: 21 + 1 = 22 (no), 49 + 1 = 50 (yes, but 50 is a multiple of 5, age next year would be 50 so current age is 49. Wait: if age next year is 50, then current age is 49. Let's check 49: 49 is a multiple of 7. Next year is 50, which is a multiple of 5. What about 21? Next year is 22, not a multiple of 5. Let's test 14: next year 15 (multiple of 5). 14 is a multiple of 7. Let's check 84? Younger than 80. Let's check multiples of 7: 14, 28, 42, 56, 70. Add 1: 15 (yes), 29 (no), 43 (no), 57 (no), 71 (no). So 14 is a valid answer. Let's check 14: age 14 is a multiple of 7. Next year 15 is a multiple of 5. Correct answer is 14.
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: Hard. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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