Q: What are the factor combinations of the number 640?

How do I find the factor combinations of the number 640?

Unfortunately, there's not simple formula to identifying all of the factors of a number and it can be a tedious process when trying to identify the divisors of larger numbers. To find the factor combinations of the number 640, it is easier to work with a table - it's called factoring from the outside in.

Outside in Factoring

We start by creating a table and writing 1 on the left side and then the number we're trying to find the factors for on the right side in a table. Then, below that, write the numbers as a negative as well.

1		640
-1		-640

With that explanation out of the way, let's continue. Next, we take the number 640 and divide it by 2:

640 ÷ 2 = 320

If the quotient is a whole number, then 2 and 320 are factors. In this case, the quotient is a whole number. Write them in the table inside the other two factors like the below example. Don't forget to write the negative numbers too!

Here is what our table should look like at this step:

Now, we try dividing 640 by 3:

640 ÷ 3 = 213.3333

If the quotient is a whole number, then 3 and 213.3333 are factors. In this case, the quotient is not a whole number. Don't write anything down and try the next divisor.

Here is what our table should look like at this step:

Let's try dividing by 4:

640 ÷ 4 = 160

If the quotient is a whole number, then 4 and 160 are factors. In this case, the quotient is a whole number. Write them in the table inside the other two factors like the below example. Don't forget to write the negative numbers too!

Here is what our table should look like at this step:

If you did it right, you will end up with this table:

More Examples

Here are some more numbers to try:

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