A two-digit number is four times the sum of its digits. Adding 18 to it reverses its digits. The number is:

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Accepted Answer

24. Let the number be 10a + b. From 10a + b = 4(a + b) we get 6a = 3b, so b = 2a. From 10a + b + 18 = 10b + a we get 9b − 9a = 18, so b = a + 2. Then 2a = a + 2 gives a = 2 and b = 4, i.e. 24. Check: 24 = 4 × 6 and 24 + 18 = 42.

A two-digit number is four times the sum of its digits. Adding 18 to it reverses its digits. The number is:

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