How to recognize if a number is a multiple of 9 – Quick and easy math trick

How to recognize a # as a multiple of 9

The sum of the digits is a multiple of 9.

To recognize if a number is a multiple of 9, you can use the following trick:

First, write the given number in decimal notation, and add up the digits. For example, consider the number 3603:
3 + 6 + 0 + 3 = 12

Next, add up the digits in the sum from the previous step, and continue doing this until you get a single digit:

1 + 2 = 3

If the final digit is 9, then the original number is a multiple of 9. In the example above, because the final result is 3, then 3603 is not a multiple of 9.

Let’s try this trick with a number that is a multiple of 9, such as 729:
7 + 2 + 9 = 18
1 + 8 = 9

Since the final result is 9, we know that 729 is a multiple of 9.

Therefore, using this trick can help you recognize whether a given number is a multiple of 9 or not.

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