Question

if i am not given the value of the first value in a problem, how do i find the y intercept?

Answer 1

What do you mean?

Answer 2

well, i am given 1.0 bushels, in billions, at a price of 1.35. each value of bushels increases by .5 and each relative price increases by a 1.05. this goes for 4 values up to 2.5 (billion) bushels at an ending price of 4.50. i have the slope of 2.1 but i need the y intercept or where x=0

Answer 3

Wait, was the slope given or did the problem describe how much the price went up too?

Answer 4

no, i was given a table with values. then i had to calculate the average rate of change(slope)

Answer 5

for each price, the value is constant

Answer 6

im scared you're typing for so long lol

Answer 7

Ok, yes. So you're right. Your slope is 2.1 for this problem. So the easiest thing to do is start with the form y=mx+b.
We know that m=2.1 and we're given that 1.0 bushels equals 1.35 in price.
So we can plug in 1.0 bushels for y, 1.35 for x, 2.1 for m and then solve for b.
1.0=2.1(1.35)+b
1.0=2.835+b
b=1.0-2.835
b=-1.835
I'm assuming price is plotted on the x-axis since price should start above 0 initially. So at this point, b is our y-intercept, so the coordinate pair (0, -1.835) is where your y-intercept is.

Answer 8

Lol sorry I typed so long. I usually try to think how to explain things easily before I post. Its not so easy to explain the jumbled mess in your head.

Answer 9

right, i appreciate the help!

Answer 10

Make sense?

Answer 11

but for this kind of problem you wouldn't necessarily want an x value of zero because money typically isnt negative.

Answer 12

Right! If the price started at zero it would initially be free and that doesn't make sense! So, this usually means our y-intercept is negative and slope is positive when we talk about prices per bushel, in your problem, for instance.

Answer 13

ok, so how can i test my formula?

Answer 14

The y-axis is your independent value and the x-axis is the dependent value. Here, you would want bushels to be on the y-axis since price depends on the amount of bushels.

So in the form y=mx+b, your equation is y=2.1x-1.835.
To test, look at your table of values. Plug in a y-value (number of bushels) into the equation and solve. If your answer matches the corresponding price in the table, then your formula works!

Answer 15

ummm i plugged in 1.5 bushels. 2.1*1.5-1.835=1.315 but the table at 1.5 says 2.40???

Answer 16

sorry if im wasting your time

Answer 17

Can you type the values in please? Maybe if I see them we can modify the equation to work. It appears we haven't done this right.

Answer 18

ok

Answer 19

1 bushel=1.35
1.5bushels=2.40
2bushels=3.45
4bushels=4.50

Answer 20

Hold on, I got something backwards

Answer 21

alright no problem

Answer 22

does the table label x and y

Answer 23

no its and S and P where s is the number of bushels and p is price

Answer 24

Ok, I'm assuming S for Stock, P for Price. So, it looks like your basic graph of quantity v. price in economics. so P is on the x-axis, S on the y-axis.
So, S=mP+b.
The only thing is that you then have the change in y as 1/2 and the change in x as 105/100 or 21/20. Giving m=10/21, which makes no sense.

Answer 25

it states P is on the vertical axis

Answer 26

meaning the y??

Answer 27

Ok, so that helps then. Its important to know what is on the x-axis, and what is on the y-axis, but you're right price would be on the y-axis if thats what it says.

Answer 28

So we really have P=mS+b

Answer 29

\[\frac{ y2-y1 }{ x2-x1 }=\frac{ 2.4-1.35 }{ 1.5-1 }=\frac{ 1.05 }{ .5 }=2.1\]
P=2.1S+b

Let's plug in points.
Since P = y-axis and S= x-axis, (1, 1.35) is our first point from the table.

(1.35)=2.1(1)+b
b=1.35-2.1
b=-0.75

Our equation is P=2.1S-0.75

Let's test it:

P=2.1S-0.75 with point (2, 3.45)

P=2.1S-0.75
P=2.1(2)-0.75
P=4.2-0.75
P=3.45

So the equation works!!!

Answer 30

phew, thanks a lot buddy! i was thinking to do that but i flipped the S and P around -__- thanks for your patience!

Answer 31

No problem. Just be sure to keep track of your x and y values and it will make things a lot easier. Even label write out the values as coordinate pairs and label them S and P if you have to. Whatever it takes to keep it in order.

Answer 32

right. i'll message you again if i need help?

Answer 33

Sure thing. I try to get on when I can.

Answer 34

alright