The value of a 2-digit number is 5 times the sum of the digits. What is the product of the digits?

Explanation

Let the number be 10x + y. We have 10x + y = 5(x + y) \implies 5x = 4y. Since x, y are single digits, the only valid combination is x = 4 and y = 5. Product of digits is 4 \times 5 = 20.

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