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2023 AMC 10A Problem 3

Problem 3 of 25EasierNumber Theory

How many positive perfect squares less than 20232023 are divisible by 5?5?

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Solution

If a perfect square is divisible by 5,5, it’s divisible by 25,25, so it looks like (5k)2=25k2.(5k)^2 = 25k^2. We need 25k2<2023,25k^2 \lt 2023, i.e. k2<80.9.k^2 \lt 80.9. That allows k=1,2,…,8,k = 1, 2, \ldots, 8, which is 88 squares. Thus, A is the correct answer.
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Tagged: perfect square · divisibility

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