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Math

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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(t-300)+79.95, where it is assumed that t≥300 minutes. What times will keep costs between $127.45 and $156.70?

  • Math -

    $127.45 < 0.25(t-300) + 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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