Question

Find the equation of the line in the graph and mathematically model the scenario using function notation where cost is a function of number of minutes.

Answer 1

PLEASE HELP

Answer 2

I don't know how to find the function.

Answer 3

@ganeshie8

Answer 4

Right back at you, hypocrite.

Answer 5

the function looks like a line to me...
I would find the slope: change in y divided by change in x
then find the y -intercept (what is y when x is 0)
then write
f(x) = m x + b
where m is the slope that you found, and b is the y-intercept you found

Answer 6

What he said ^
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Answer 7

@phi I don't understand

Answer 8

which part ?

do you agree it looks like a line ?

Answer 9

Yes but the line only seems to intersect the y line

Answer 10

see this http://www.khanacademy.org/math/algebra/linear-equations-and-inequalitie/slope-and-intercepts/v/slope-of-a-line

Answer 11

Okay

Answer 12

Ohhh I get it.

Answer 13

what do you get for the slope ?

Answer 14

I finished the video and I see what he did, but I still need to figure out my problem. This will take a minute or two . . .

Answer 15

I got 1/4

Answer 16

right idea... but you have to use the numbers they gave you.
4 "boxes" on the x-axis is 400 steps
1 "box" on the y-axis is 20

Answer 17

Oh so I have 400/80??

Answer 18

can you see that y starts at 20 and goes up to 40 ? what is the change in y ?
can yo see that x starts at 0 and goes up to 400 ? what is the change in x?

Answer 19

Yes so y changes 20, and x changes 400.

Answer 20

So in 400 minutes the cost of the phone is $40

Answer 21

yes, and slope= change in y over change in x = 20/400
you can simplify that to 2/40 or 1/20

the slope is 1/20

the y-intercept is the y value when x is 0. can you read that number off the graph ?

Answer 22

So the y-intercept is 20?

Answer 23

But the question wants me to create an equation for the graph

Answer 24

yes, now use m= 1/20 and b= 20 in
f(x) = m x + b

this will be the equation of the line

Answer 25

So the equation is f(x) = 1/20x + 20 ??

Answer 26

But the question wants me to create an equation for the graph

Answer 27

So the y-intercept is 20?

Answer 28

So the equation is f(x) = 1/20x + 20 ??

yes but I would write it
f(x) = (1/20) x + 20
just to make it clear it is 1/20 times x and not 1 divided by (20x)

as a test, if we try x=200 we get
f(200)= (1/20) * 200 + 20
1/20 times 200 is 10
f(200) = 10+20 = 30
if we look at the graph, we see the y value (or f(x) value) when x=200 is 30
it works!