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Divisibility · Beginner

Divisibility by 9

Add the digits. If the sum is divisible by 9, the number is divisible by 9.

01

The fast method

⚡

7 + 2 + 9 = 18; therefore 729 is divisible

How it works

For 729, 7+2+9=18, which is divisible by 9.

02

Why it works

Every power of 10 leaves remainder 1 modulo 9.
Use it when

Applies to whole numbers.

Watch out for

Use the absolute value for negative whole numbers.

03

Verified examples

Example 1

Is 729 divisible by 9?

7+2+9=18; 18 is divisible by 9

Yes
Example 2

Is 5832 divisible by 9?

5+8+3+2=18

Yes
Example 3

Is 721 divisible by 9?

7+2+1=10

No