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Problem 236

Algebra Difficulty 1.5 Multiple choice CEMC Gauss (Grade 8) · Canada · 2023

A list of 5 integers repeats to form the pattern: $4, -3, 2, -1, 0, 4, -3, 2, -1, 0, \ldots$
What is the sum of the first 23 integers?

Pick one

Official solution

The prime numbers that are less than 10 are $2,3,5$ , and 7.

Thus, the only two different prime numbers whose sum is 10 are 3 and
7.

The product of these two numbers is $3\times7=21$ .

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.