00:01
A recipe says that for every five cups of flour, you have to use two cups of sugar.
00:08
And so we have to figure out how much sugar for one cup of flour, how much flour for one cup of sugar, how much flour for seven cups of sugar, and how much sugar for six cups of flour.
00:23
And so the way we're going to solve this is we are going to set up a proportion and solve it using cross multiplication.
00:31
Okay, so no matter what, five cups of flour, so we'll denote that as five cup f.
00:40
Five cups of flour requires two cups of sugar.
00:50
Equals, let's do the first one here.
00:54
For one cup of flour, if we have one cup of flour, how much sugar do we need? we don't know how much sugar, so i'm putting that as a value of x.
01:08
So now we're going to do some cross multiplication.
01:11
The way we do that is we're just going to cross this right here like that, and we're going to multiply across the equal sign.
01:18
So 5 times x is 5x.
01:23
Let's write this down here, 5x.
01:29
And then we're going to cross multiply over on this side.
01:34
And this is going to be 1 times 2, which is just...
01:41
So just so that way we have space, i'm going to move this right here.
01:45
Over to this side, 5x equals 2.
01:49
So let me just erase this.
01:52
Perfect.
01:54
Okay, 5x equals 2.
01:56
We need to solve for that x.
01:59
So we're going to divide both sides by 5.
02:04
And here this gives us that x equals 2.
02:10
So if there's one cup of flour, you need two cups of sugar.
02:17
Now let's figure out what if we have one cup of sugar.
02:23
So we have our proportion.
02:25
5 cups of flour for 2 cups of sugar...