Question 131969: I really need help with this word problem. I've been working on it for 2 hours and keep getting wrong answers.
Problem
A cellular phone co. offers a contract for which cost C in dollars, of t minutes of telephoning is given by C=0.25(t-400)+64.95, where it is assumed that t>400 minutes. What times will keep costs between $105.20 and $146.45, the telephoning times must be between ____ minutes and ______ minutes.
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! A cellular phone co. offers a contract for which cost C in dollars, of t minutes of telephoning is given by C=0.25(t-400)+64.95, where it is assumed that t>400 minutes. What times will keep costs between $105.20 and $146.45, the telephoning times must be between 561 minutes and 726__ minutes.
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C(t) = 0.25(t-400)+64.95
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Solve the following :
105.20 < 0.25(t-400)+64.95 < 146.45
Subtract 64.95 along the line to get:
40.25 < 0.25(t-400) < 81.5
Divide thru by 0.25 to get:
161 < (t-400) <326
Add 400 along the line to get:
561 < t < 726
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Cheers,
Stan H.
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