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?

Answer 1

Monthly cost of cell phone for 0 minutes is $19.95 and for 40 minutes of talk is $21.95.

It means that average rate of change ( increase of monthly cost for each minute of talk time ) is: ARC = ( 21.95 - 19.95 ) / ( 40 - 0 ) = 2.00 / 40 = $0.05.

Answer 2

The monthly change is $ 0.70

Explanation:

From the statement, it can be seen that the average monthly change is $ 0.70. This can be derived from the following:

From 0 to 10 minutes, the difference was: $ 10.65 - $ 9.95 = $ 0.70

Then from 10 to 20 minutes, the difference was $ 11.35 - $ 10.65 = $ 0.70

In this way, the average difference was consistent throughout, that is, $ 0.70 increase in every 10 minutes.