But what if we try to divide 24 by a number that ISN’T one of our factors; like the number 7?
If we try 24 divided by 7 on a calculator, we get 3.42857… blah, blah, blah … a long decimal number.
That didn’t divide in evenly because there’s a big remainder!
What we just did is called “testing for divisibility”.
Testing for divisibility is a way to find out if a number is a factor of another number.
With the test we just did, we confirmed that 4 is a factor of 24 but 7 is not.
Sometimes you may be asked to find ALL the factors of a number.
If that happens, you can use testing for divisibility to solve the problem.
To see how it works, let’s try to find ALL the factor or 24.
We already know four of them, but there’s a lot more numbers we can test.
Fortunately, we only need to test numbers that are less than half of the number we’re testing.
And since half of 24 is 12, we just need to test the numbers 1 thru 12.
To keep things organized, let’s list the numbers we are gonna test
and we'll circle the factors that we already know: 3, 4, 6, and 8.
We can also cross out the 7 since we already tested it and found out it wasn’t a factor.
Okay, now for the numbers we haven’t tested yet. Let’s start with 1.
Well of course 1 is a factor, because 1 will divide evenly into ANY whole number.
So 1 is always a factor.
And since 1 is a factor, then that means 24 is also a factor because 1 × 24 = 24.
It might seem weird that a number is always a factor of itself, but it’s true.