SOLUTION: How do you solve a linear equation when the constant isn't given? For example: Lisa can not remember which long distance plan she has with her phone company. However, she knows th

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: How do you solve a linear equation when the constant isn't given? For example: Lisa can not remember which long distance plan she has with her phone company. However, she knows th      Log On


   



Question 268626: How do you solve a linear equation when the constant isn't given?
For example: Lisa can not remember which long distance plan she has with her phone company. However, she knows that she pays a basic monthly fee and a rate per minute for long distance calls. In June her bill was 53.95 for 120 minutes of long distance calls. In July it was 68.55 for 412 minutes

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
You are given 2 points in the form (x,y)
where x is minutes and y is the monthly bill
The 2 points also give you the slope of the line
as (change in y)/(change in x)
Use the point slope formula

(x1,y1) = (120,53.95)
(x2,y2) = (412,68.55)
%28y+-+53.95%29%2F%28x+-+120%29+=+%2868.55+-+53.95%29%2F%28412+-+120%29
%28y+-+53.95%29%2F%28x+-+120%29+=+14.6%2F292
y+-+53.95+=+.05%2A%28x+-+120%29
y+-+53.95+=+.05x+-+6
y+=+.05x+%2B+47.95
Even when there are no minutes there is a charge
of $47.95 for each monthly bill
She pays 5 cents per minute