SOLUTION: Cell Phone Service Sprint PCS offers a monthly cellular phone plan for 35$. It includes 300 anytime minutes and charges $0.40 per minute for additional minutes. The following fu

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Question 264951: Cell Phone Service Sprint PCS offers a monthly cellular phone plan for 35$. It includes 300 anytime minutes and charges $0.40 per minute for additional minutes. The following function is used to compute the montly cost for a subscriber.
It gives you the function

C(X)={ 35 if 0 is greater than X and less than or equal to 300
{0.40x-85 if x is greater than 300
my teacher wants to know why you have to minus 0.40x by 85?
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Cell Phone Service Sprint PCS offers a monthly cellular phone plan for 35$. It includes 300 anytime minutes and charges $0.40 per minute for additional minutes. The following function is used to compute the montly cost for a subscriber.
It gives you the function
C(X)=(35 if 0 <= X <= 300
{0.40x-85 if x > 300
my teacher wants to know why you have to minus 0.40x by 85?
----------------------
If x > 300, C(x) = 0.40*(300 + x) = $120 + 0.40x
The customer should not be charged 120 for the 1st 300 minutes
since they were free. So $85 is subtracted from the charge.
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Cheers,
Stan H.