Question

A 5-mile cab ride costs $7.20. A 9-mile cab ride costs $11.60. Find a linear equation that models a relationship between cost c and distance d.


c = 1.44d + 4.40
d = 1.10c + 4.40
c = 1.29d + 1.70
c = 1.10d + 1.70

Answer 1

let cost be a function of distance so (cost,distance)

we have two points :

(5,7.20) , (9,11.60)

using two points.. can you calculate slope ?

Answer 2

slope = 1.1 ?

Answer 3

very good!

lets call the slope m.
now use one of the points and get the line equation
since we treat y as c (cost) and x as d (distance)
the line equation is given by

c = c1 + m(d-d1)

where d1,c1 are the coordinates of one of your points

Answer 4

So, would it be written like this?
c = 7.20 + 1.1(d-9)

Answer 5

you have to choose one of the points :

(5,7.20) or (9,11.60)

you dont mix between them

Answer 6

I don't know which ones to choose?

Answer 7

it doesnt matter .. pick one point and it will be your (d1,c1)

Answer 8

eventually you will get the same answer.. no matter which of the point you choose

Answer 9

So , it will be

C = 7.20 + 1.1(d-5)

Answer 10

yes ! its good