Question

Raj is deciding between two cell phone plans, A and B, which are both linear functions. The monthly charge for plan A according to the number of minutes used is shown in the table.

Monthly Charge for Plan A
Minutes used, x
Monthly charge ($), y
0
14.45
3
14.84
6
15.23
9
15.62
12
16.01

Plan B has the same monthly base charge as plan A, but it charges a different amount per minute used. If the total monthly charge for plan B is $22.10 when 45 minutes are used, what is the slope of the linear function that represents the cost of plan B?
0.13
0.17
0.39
0.45

Answer 1

Plan A's base charge is the y-intercept 14.45. Plan B has the same base, and at 45 minutes costs 22.10, so its per-minute rate is
m = (22.10 − 14.45) / 45 = 7.65 / 45 = 0.17.
Answer: 0.17