Take ANY number, subtract the digits in that number, and the answer is divisible by 9.

14… 14 – 1 – 4 = 9

25… 25 – 2 – 5 = 18

36… 36 – 3 – 6 = 27

49… 49 – 4 – 9 = 36

1,234… 1,234 – 1 – 2 – 3 – 4 = 1,224

And you don’t need your calculator to figure out if 1224 is divisible by 9, it is. How do I know? Add 1 + 2 + 2 + 4 together and if it’s 9 or divisible by 9, then the number is also divisible by 9.

7,692… 7,692 – 7 – 6 – 9 – 2 = 7,668

And then 7 + 6 + 6 + 8 = 27 which is divisible by 9 so 7,668 is divisible by 9 (= 852).

I love Math.