4
QuizMultiple Choice

Exploring Slope

Question 4 • WCPSS-Introductory Math CR

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 AMinutes used, xMonthly charge ($), y014.45314.84615.23915.621216.01Plan 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?

Answer
A
0.13
B
0.17
C
0.39
D
0.45

Explanation

Plan A’s monthly base charge is $14.45, shown when 0 minutes are used. Plan B has the same base charge, so its cost increases by $22.10 − $14.45 = $7.65 over 45 minutes. Its slope is $7.65 ÷ 45 = $0.17 per minute, so the correct choice is 0.17.

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