0:00
All right.
00:01
So in this problem, we have a demand for gasoline, and it's modeled by a linear function of the price.
00:07
Knowing that it's a linear function is important in this problem.
00:12
So it tells us the price of gasoline is $3 .20.
00:17
The quantity demanded is 72 gallons.
00:20
If it raises up to $3 .50 per gallon, the demand falls to 60 gallons in that period.
00:29
Okay.
00:29
So to find our function, it's linear.
00:33
It's going to be in the form mx plus b.
00:37
Okay, m is the slope, and b is the, and b is the, well, y intercept.
00:47
We're using q and p.
00:50
So p is like our x coordinate, q is our y coordinate.
00:56
It.
00:57
All right.
00:57
So to find the slope, right? it's the, so it's y2 minus y1.
01:04
We know that the second y coordinate is 60.
01:09
The first y coordinate is 72.
01:12
Those are the quantities.
01:14
The second price is $3 .50.
01:18
The first price is $3 .20.
01:21
So that's a change of negative 12 over and then over 30 cents over 0 .3 .30 cents.
01:34
Okay.
01:35
So when we divide that in, we're going to get negative 40.
01:47
Negative 40.
01:50
Okay, so what that means, so that's our slope.
01:54
We're going to talk about the significance of that in a second.
01:59
Okay.
02:00
Now, we've got to figure out what b is.
02:02
Well, now that our slope is b, if i put $3.
02:06
And 50 cents if i go to you of three dollars and fifty cents and i put three dollars and fifty cents here for p well i know at three dollars and fifty cents our demand is sixty we know we only want sixty dollars here or sixty gallons of gas that's from the problem so to find b just kind of multiply this out right here and we get, was that 120 plus 20? so 140, negative 140.
02:49
Add that to both sides.
02:53
And we get 200.
02:54
So 200 equals b.
02:56
So here's my function in slope intercept form right there.
03:03
Okay.
03:04
So what that means is, and we're going to get to that.
03:09
We'll get to that on the next couple questions.
03:12
So let's draw a little graph so you can kind of see what this looks like...