Question 208197: A cellular phone company offers a contract for which the cost , C, in dollars, of t minutes of telephoning is given by C = .25(t – 600) + 65.95 , where it is assumed that t ≥ 600 minutes. What times will keep costs between $110.95 and $145.95?
For the cost to be between $110.95 and $145.95, the telephoning time must be between ___ minutes and ___ minutes.
Thank you, in advance. Your assistance is vey much appreciated.
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website! A cellular phone company offers a contract for which the cost , C, in dollars, of t minutes of telephoning is given by C = .25(t – 600) + 65.95 , where it is assumed that t ≥ 600 minutes. What times will keep costs between $110.95 and $145.95?
:
Solve two inequalities
.25(t - 600) + 65.95 > 110.95
.25t - 150 + 65.95 > 110.95
.25t - 84.05 > 110.95
.25t > 110.95 + 84.05
.25t > 195
t > 
t > 780 minutes
and
.25(t - 600) + 65.95 < 145.95
.25t - 150 + 65.95 < 145.95
.25t - 84.05 < 145.95
.25t < 145.95 + 84.05
.25t < 230
t < 
t < 920 minutes
For the cost to be between $110.95 and $145.95, the telephoning time must be between 780 minutes and 920 minutes.
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