2026 AMC 8 Problem 18

Attempt Problem 18 of the 2026 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 2026 AMC 8 solutions, or check the answer key.

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

18.

In how many ways can 6060 be written as the sum of two or more consecutive odd positive integers that are arranged in increasing order?
11
22
33
44
55
Answer: B
Concepts:arithmetic sequencedivisibilitycasework
Small hint:
Write the terms as a,a+2,…,a+2(k−1)a,a+2,\ldots,a+2(k-1)
Big hint:
Their sum is k(a+k−1)k(a+k-1), so kk must divide 6060
Video solution:
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Written solution:
Suppose there are k≥2k\ge2 terms, starting with odd positive integer aa. The sum is a+(a+2)+⋯+(a+2k−2)a+(a+2)+\cdots+(a+2k-2) =k(a+k−1)=k(a+k-1) =60=60. Testing divisors kk of 6060, the positive odd starts occur for k=2k=2, giving 29+3129+31, and for k=6k=6, giving 5+7+9+11+13+155+7+9+11+13+15. Thus there are 22 ways.
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