SOLUTION: the monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes). The monthly cost for 55 minutes of calls is $17.32 and th

Algebra ->  Coordinate Systems and Linear Equations  -> Lessons -> SOLUTION: the monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes). The monthly cost for 55 minutes of calls is $17.32 and th      Log On


   

Question 1061687: the monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes). The monthly cost for
55 minutes of calls is $17.32 and the monthly cost for 89 minutes is 20.38 What is the monthly cost for 65 minutes of calls?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
x for time and y for cost

Points (x,y)

format system as mx%2Bb=y;

system%2855m%2Bb=17.32%2C89%2Am%2Bb=20.38%29
Ready to eliminate b using Elimination Method to find value for m.

34m=20.38-17.32
m=0.09
-
b=17.32-55m
b=17.32-55%280.09%29
b=12.37

-
USE THE FORMULA highlight%28y=0.09x%2B12.37%29.