In this week's math trick, we have another divisibilty trick that skips the long division! This time, we will be tackling 9's.
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There's an easy and fun way to tell if a number is divisible by 9! Simply add all the digits of the number and then divide by 9. If the digits add to a multiple of 9, then the number is divisible by 9! In our example, we use 738.
7 + 3 + 8 = 18
and 18 is a multiple of 9
therefore, 738 is divisible by 9!
For larger numbers, you can also repeat this step you are left with a single digit number. If you end up with 9, then the number is divisible by 9.
For instance, 322,867
3 + 2 + 2 + 8 + 6 + 7 = 28
28 is not divisble by 9 – but let's say we are not sure of that.
2 + 8 = 10
1 + 0 = 1
1 ≠ 9
Therefore, 322,867 is not divisible by 9.
Think you got the hang of it? Test out your new math trick with the sample questions below!
