 Mathematics
20 April, 22:15

# Which of these numbers are exactly divisible by 9? 107,513,944,126,80

0
1. 20 April, 22:42
0
513 and 126 both are. (The question doesn't say

that there's only one of them in the list.)

Here's an easy way to tell: (I don't know how or why it works,

but it works.)

You're looking at a big number, and you need to find out if it's

divisible by 9.

Here's the two-step process:

- - If it's going to be divisible by 9, then it has to be divisible by 3.

- - Find out whether it's divisible by 3. If it is, then ...

- - Find out whether it's divisible by 9.

Step 1:

Add up all the digits in the number. If that sum is divisible by 3,

then the original big number is too.

Example:

Is 549 divisible by 3?

Add up its digits: (5 + 4 + 9) = 18.

Is 18 divisible by 3?

Yes. That tells you that 549 is divisible by 3.

So it could be divisible by 9.

Step 2:

Take that same 18 and add up its digits.

(1 + 8) = 9.

9 is divisible by 3.

This tells you that the original big number ... 549 ... is also divisible by 9.