Question

I thought of a 2-digit number. It's a multiple of 9 and the sum of its digits is five times smaller than the number itself. What is my number?

Answer 1

Step-by-step explanation:

Since the sum of the digits must be an integer, the number itself must also be a multiple of 5.

Lowest common multiple of 5 and 9 = 45.

Therefore the number could be 45 or 90.

5(9 + 0) =/= 90, so 90 is incorrect.

Since 5(4 + 5) = 45, 45 is the answer.