Question

The monthly cost of driving a car depends on the number of miles driven. Lynn found that in May her driving cost was $380 for 580 mi and in June her cost was $460 for 900 mi. Assume that there is a linear relationship between the monthly cost C of driving a car and the distance driven d.

(a) Find a linear equation that relates C and d.


(b) Use part (a) to predict the cost of driving 1700 mi per month.

(c) Draw the graph of the linear equation.

Answer 1

alright which do you think would be the dependent variable?

Answer 2

c or d?

Answer 3

C

Answer 4

alright so that'll be our "y"
and d will be our "x"

Answer 5

(580,380) and (900, 460)

Answer 6

Can you find the slope?

Answer 7

.25

Answer 8

Alright, same as 1/4.

Now using the slope and one of the points we can write slope point form. which point do you want to use?

Answer 9

Still there?

Answer 10

yes

Answer 11

(580,380)

Answer 12

Alright. are you familiar with point slope form?

Answer 13

\[y-y _{_{0}}=m(x-x _{0})\]

Answer 14

In our case we use c for y and d for x

Answer 15

So we get

c-380=1/4(d-580)

Answer 16

Distribute the 1/4 and we get

c-380=1/4d-145

Answer 17

f(c)=4c-940

Answer 18

Add 380 to both sides and we get:
c=1/4d+235

Answer 19

understand so far?

Answer 20

yah so what is the final equation?

Answer 21

a) Find a linear equation that relates C and d.

Answer 22

c=1/4d+235 is the answer to a

Answer 23

Ready to do b?

Answer 24

yes!

Answer 25

wait i got part b :)

what does the graph look like?

Answer 26

Hmm, well the y intercept is (0,235)

Answer 27

can u please graph it