2026 AIME II Problem 1

Below is the professionally curated solution for Problem 1 of the 2026 AIME II, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2026 AIME II solutions, or check the answer key.

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Concepts:arithmetic sequencedivisibilitygreatest common divisor

Difficulty rating: 1840

1.

Find the sum of the 1010th terms of all arithmetic sequences of integers that have first term equal to 44 and include both 2424 and 3434 as terms.

Solution:

Let the common difference be d.d. Since the first term is 44 and both 2424 and 3434 appear, dd divides 244=2024 - 4 = 20 and 344=30,34 - 4 = 30, so dd divides gcd(20,30)=10.\gcd(20, 30) = 10. The difference must be positive to reach 2424 and 3434 from 4,4, so d{1,2,5,10}d \in \{1, 2, 5, 10\} (and each of these works, since d20d \mid 20 and d30d \mid 30 put both targets in the sequence).

The 1010th term is 4+9d,4 + 9d, so the requested sum is d{1,2,5,10}(4+9d)=44+9(1+2+5+10)=16+162=178.\sum_{d \in \{1,2,5,10\}} (4 + 9d) = 4 \cdot 4 + 9(1 + 2 + 5 + 10) = 16 + 162 = 178.

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