2012 AMC 8 Problem 15

Attempt Problem 15 of the 2012 AMC 8 below, then check your answer against the video solution and professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2012 AMC 8 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

15.

The smallest number greater than 22 that leaves a remainder of 22 when divided by 3,3, 4,4, 5,5, or 66 lies between what numbers?
4040 and 5050
5151 and 5555
5656 and 6060
6161 and 6565
6666 and 9999
Answer: D
Concepts:least common multiplemodular arithmetic
Small hint:
Subtract 22 from the unknown number.
Big hint:
The result must be a common multiple of 33, 44, 55, and 66.
Video solution:
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Written solution:
Let the number be x.x. Since it leaves a remainder of 22 when divided by 33, 44, 55, and 6,6, we know x−2x-2 is a multiple of 33, 44, 55, and 6.6. This means x−2x-2 is a multiple of lcm⁡(3,4,5,6)\operatorname{lcm}(3,4,5,6), which is 60.60. Therefore, x−2x-2 must be a multiple of 60.60. The next number such that this occurs is when x−2=60  ⟹  x=62.x-2 = 60 \implies x = 62 .
Thus, the answer is D .
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