Is this the multiples of nine 162 or 163?

Answer 1

If a number is a multiple of nine, its digit root (the sum of its digits until the answer is only one digit long) is 9 (for multiples of 3, this is the case if the digital root is 3, 6 or 9).

For 163, 1 + 6 + 3 = 10. 1 + 0 = 1 so the digital root is 1 and therefore 163 is not a multiple of 9.

However, for 162, 1 + 6 + 2 = 9 so the digital root is 9 so 162 is a multiple of 9 (18 x 9 = 162).