Chapter 6.3, Problem 11E

To determine

To calculate: the more minutes you can talk long distance when there is $\$1.21$ left on your calling card.

Answer to Problem 11E

The more minutes you can talk long distance are $22$ minutes.

Explanation of Solution

Given information: You already made a call for $12$ minutes which cost $\$.66$ and there is $\$1.21$ left on your calling card. Long distance calls’ cost per minute is constant.

Calculation :

To find out the number minutes you can talk long distance when there is $\$1.21$ left on your calling card, let $m=\text{the more minutes you can talk for with the money left}$ .

Therefore, $\frac{\text{cost of the phone call you made}}{\text{minutes of that phone call}}=\frac{\text{amount of money left on your calling card}}{m}$

  $\begin{array}{l}\frac{0.66}{12}=\frac{1.21}{m}\text{ [Write the proportion}\text{.]}\\ 0.66\times m=12\times 1.21\text{ [Apply cross products property}\text{.]}\\ 0.66m=14.52\text{ [Multiply}\text{.]}\\ \frac{0.66m}{0.66}=\frac{14.52}{0.66}\text{ [Divide each side by 0}\text{.66 to place the variable on one side of the equation}.]\\ m=22\text{ [Simplify}\text{.] }\end{array}$

Hence, you can talk long distance for $22$ minutes more using your calling card.