‘Moreover, if you multiply nine by any whole number except zero, and repeatedly add the digits of the answer until it’s just one digit, you will end up with nine. For example, 2 multiplied by 9 is 18. 1 when added to 8 is 9. Take a bigger number, say, 5,78,329. When multiplied by nine, the answer is 52,04,961. And 5 + 2 + 0 + 4 + 9 + 6 + 1 is 27, and 2 + 7 is 9. Conversely, if the digits of a number add up to nine or a multiple of nine, then the number itself must be a multiple of nine.
