Question

2. How do you know if a number is
divisible by 9 without dividing?

Answer 1

If the sum of all the digits of a number is divisible by 9, then the number is also divisible by 9. examining its digits.

Answer 2

Add all the digits of the number, then check if that sum is divisible by 9. If yes, we know the number is divisible by 9.