Concept explainers
International Calling A cell phone company offers an international plan by charging for the first 80 minutes, plus for each minute over 80.
a. Write a linear model that relates the cost , in dollars, of talking minutes, assuming .
b. What is the cost of talking 105 minutes? 120 minutes?
To calculate:
a. Write a linear model that relates the cost , in dollars, of talking minutes, assuming .
b. What is the cost of talking 105 minutes? 120 minutes?
Answer to Problem 50AYU
Solution:
a.
b. The cost of talking for 105 minutes will be .
The cost of talking for 120 minutes will be .
Explanation of Solution
Given:
The cell phone company charges for the first 80 minutes, plus for each minute over 80.
Formula Used:
A linear equation is of the form , where is the average rate if change of that function and is the , which is the initial value of the function when .
Calculation:
Here, we can see that is the initial charge of the plan until 80 minutes.
Let the number of minutes talked be , where .
Therefore, for each , is added to the charge.
a.
Thus, the charge of the plan will be
b.
Here, we have .
Therefore, the extra minutes talked will be .
Thus, when we have , the rent of the plan will be
Therefore, the cost of talking for 105 minutes will be .
Here, we have .
Therefore, the extra minutes talked will be .
Thus, when we have , the rent of the plan will be
Therefore, the cost of talking for 120 minutes will be .
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