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minasotpen1253
01.06.2021 •
Mathematics
What’s the inequality that fits the graph
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Ответ:
The remaining credit after 75 minutes of calls is $20.9515.
Step-by-step explanation:
The amount of credit remaining on a phone card can be modeled by the following linear function:
In which C(t) is the amount remaining after t minutes, C(0) is the initial amount and a is the cost of each minute.
We take what the problem gives us, and find an expression for C(t), solving a system of equations.
The remaining credit after 40 minutes of calls is 25.20
This means that![C(40) = 25.20](/tpl/images/0513/3191/78875.png)
So
The remaining credit after 68 minutes of calls is 21.84.
This means that![C(68) = 21.84](/tpl/images/0513/3191/a98a9.png)
So
So we have to solve the following system of equations:
From the first equation, we have that:
Replacing in the second one:
We also know that
So
What is the remaining credit after 75 minutes of calls?
This is C(75).
The remaining credit after 75 minutes of calls is $20.9515.