Posted by Loli on Sunday, December 18, 2011 at 1:35pm.
A cellular phone company offers a contract for which the cost C, in dollars, of t minutes of telephoning is given by C=0.25(t300)+79.95, where it is assumed that t≥300 minutes. What times will keep costs between $127.45 and $156.70?

Math  Henry, Tuesday, December 20, 2011 at 7:34pm
$127.45 < 0.25(t300) + 79.95 < $156.70
127.45 < 0.25t  75 + 79.95 < 156.70,
127.45 < 0.25t + 4.95 < 156.70,
127.45  4.95 < 0.25t < 156.70  4.95,
122.50 < 0.25t < 151.75,
490 < t < 607.
Therefore, values of t between 490 and
607 minutes will hold the cost between $127.45 and 156.70.
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