How to Know if a Number is Divisible by 9. Math is a part of everyday life, used for everything from music notation to construction work. In fact, math and numbers can be construed as the very key to unlocking the mystery of life itself. As such, everyone at some point needs to learn how to easily divide numbers. All you need is a basic understanding of simple addition. Here is an incredibly easy way to tell if any integer is divisible by 9, using the number 189 as an example.
Use addition to add every single digit in your number together. (189 = 1 + 8 + 9 = 18)
Add the numbers together again, if the sum is higher than 10. (18 = 1 + 8)
Repeat steps 1 and 2 as many times as you need, until you get a single number. (9)
Find out what that single number is. The original number is divisible evenly only if your end sum is nine. In this example, 189 would be divisible by 9 because the single number was 9.
The example used here (189) is merely that, an example. You can use this shortcut with any integer in existence.