SOLUTION: The credit remaining on a phone card (in dollars) is a linear function of the total calling time made with the card (in minutes). The remaining credit after 20 minutes of calls is
Question 1194794: The credit remaining on a phone card (in dollars) is a linear function of the total calling time made with the card (in minutes). The remaining credit after 20 minutes of calls is $21.80, and the remaining credit after 33 minutes of calls is $19.72 . What is the remaining credit after 40 minutes of calls? Answer by ikleyn(52928) (Show Source):
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The credit remaining on a phone card (in dollars) is a linear function
of the total calling time made with the card (in minutes).
The remaining credit after 20 minutes of calls is $21.80,
and the remaining credit after 33 minutes of calls is $19.72 .
What is the remaining credit after 40 minutes of calls?
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From the post, the price for one minute call is
= 0.16 dollars.
So, we take the amount at the credit card of $21.80 after 20 minutes,
and subtract from it the cost of (40-20) = 20 minutes
21.80 - 20*0.16 = 18.60.
ANSWER. The remaining credit after 40 minutes of calls is $18.60.
