Question

Let M be a 2015-digit number that is divisible by 9. Denote the sum of the digits of the number M by A, the sum of the digits of the number A by B, and the sum of the digits of the number B by C. What is the number C?

Answer 1

That's an intriguing problem! Let's solve it step by step.

A number is divisible by 9 if the sum of its digits is divisible by 9. Since M is a 2015-digit number, the maximum sum of its digits (A) would be 2015*9 = 18135.

The sum of the digits of A (B) would be 1+8+1+3+5 = 18.

Finally, the sum of the digits of B (C) would be 1+8 = 9.

So, the number C is 9. Isn't math fascinating?