00:01
All right, in this problem, we are asked to find the greatest common factor, or gcf, of 12x plus 20.
00:07
And so i'm going to use the strategy double division or upside down division to find the common factors of 12x and 20.
00:20
To begin with, i'm going to look at the variables.
00:23
I notice that they don't both have variables, which means i cannot put a variable in the common factors, since it's not in common.
00:29
So then i can just focus on the numbers, 12 and 20.
00:33
Some numbers that come to mind are i know that 12 can be made with 2 and so can 20.
00:38
I also know that 12 could be made using 4 and so can 20.
00:44
So i could use 2 or 4.
00:46
Now, in previous examples that i've shown, i've always done the highest number that i can think of.
00:50
But i'm going to show what would happen if you did not think of that and show how powerful this particular strategy is for finding the greatest common factor.
00:58
So let's say that two was the biggest i could think of right now.
01:02
I would divide each of the terms by two and see what happens.
01:06
So two goes into 12, six times.
01:08
The answer goes below.
01:10
The x drops down because i didn't divide any x's out, plus two goes into 20, 10 times.
01:18
And so i'll place my 10 here.
01:20
Now i'm at the next level of double division.
01:23
So at this level, i'm going to see what makes these numbers.
01:27
I know that i can count by twos to get to six, and also to 10.
01:30
And so i'm going to put a two on the outside again...