For how many integers with is divisible by 5?
Solution
First, we factor as . If or , then the factor is a multiple of 5, so the original expression is divisible by 5. If or , then the factor is a multiple of 5, so the original expression is divisible by 5. If , then neither nor is a multiple of 5. Since neither factor is a multiple of 5, which is a prime number, then the product is not divisible by 5. Therefore, there are four integers in the range for which is divisible by 5.
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