Chapter 8.5, Problem 47E

To determine

To write and graph:

An equation that approximates your remaining calling time y (in minutes) after x weeks.

Answer to Problem 47E

Our required equation would be $y=500-25x$ .

Explanation of Solution

Given:

You buy a prepaid phone card that has 500 minutes of calling time. You use about 25 minutes of calling time per week.

Concept used:

We know that slope-intercept form of an equation is $y=mx+b$ , where m represents slope and b represents the y -intercept.

Calculation:

Let x represent number of weeks and y represent calling minutes.

We have been given that you use about 25 minutes of calling time per week, so minutes of calling time used in x weeks would be $25x$ .

The number of total minutes left after x weeks would be total minutes minus $25x$ . We can represent our given information in an equation as:

$y=500-25x$

Therefore, our required equation would be $y=500-25x$ .

Upon graphing our given equation, we will get our required graph as shown below: