Question 1029252: 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
42
minutes of calls is
$23.28
, and the remaining credit after
65
minutes of calls is
$19.60
. What is the remaining credit after
77
minutes of calls?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! 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
42
minutes of calls is
$23.28
, and the remaining credit after
65
minutes of calls is
$19.60
. What is the remaining credit after
77
minutes of calls?
------------------------
You have two points:: (42,23.28) and (65,19.60)
slope = (19.6-23.28)/(65-42) = -0.16
Form:: y = mx + b
Solve for "b"::
23.28 = -0.16*42 + b
b = 30
------
C(x) = -0.16x + 30
---
C(77 min) = -0.16*77 + 30 = $17.68
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Cheers,
Stan H.
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