The sum of the digits of a two-digit number is 9. Also, nine times this number is twice the number obtained by reversing the order of its digits. Then the number is

Explanation

Let the number be 10a + b. Then a + b = 9. Its reverse is 10b + a, and the condition gives 9(10a + b) = 2(10b + a). Thus 88a = 11b, so b = 8a. Combining this with a + b = 9 gives a = 1 and b = 8, hence the number is 18.