Question

A cell phone plan has a monthly cost that is shown in the table below. What is the correct statement regarding the average rate of change during the 40-minute time of talk?

Total minutes of talk time Monthly cost of cell phone
0 $19.95
10 $20.45
20 $20.95
30 $21.45
40 $21.95


A.) The average rate of change is $0.50, meaning that for each minute of talk time, the monthly bill increases by $0.50.

B.) The average rate of change is $0.50, meaning that for every ten minutes of talk time, the bill increases by $0.50.

C.) The average rate of change is $0.05, meaning that for each minute of talk time, the monthly bill increases by $0.05.

D.) The average rate of change is $0.05, meaning that for every ten minutes of talk time, the bill increases by $0.05.

Answer 1

The answer would be B The average rate of change is $0.50, meaning that for every ten minutes of talk time, the bill increases by $0.50. 

Answer 2

For this case, the first thing we must do is find the average rate of change for the mentioned interval.

By definition we have to:

$AVR = \frac{f(x2)-f(x1)}{x2-x1}$

Substituting values we have:

$AVR = \frac{21.95-19.95}{40-0}$

Rewriting we have:

$AVR = \frac{2}{40}$

$AVR = \frac{1}{20} AVR = 0.05$

Answer:

C.) The average rate of change is $0.05, meaning that for each minute of talk time, the monthly bill increases by $0.05.