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The remaining on a phone card (in dollars) is a linear function of the total calling time made with the card (in minutes). The remaining credit after 35 minutes of calls is $15.10, and the remaining credit after 73 minutes of calls is $9.78. What is the remaining credit after 94 minutes of calls?

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  1. 6 July, 07:33
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    Answer: the remaining credit after 94 minutes of calls is $6.84

    Step-by-step explanation:

    let x represent the total calling time made with the card.

    Let y represent the remaining amount of credit on the card

    If we plot y on the vertical axis and x on the horizontal axis, a straight line would be formed. The slope of the straight line would be

    Slope, m = (9.78 - 15.1) / (73 - 35)

    m = - 5.32/38 = - 0.14

    The equation of the straight line can be represented in the slope-intercept form, y = mx + c

    Where

    c = intercept

    m = slope

    To determine the intercept, we would substitute x = 35, y = 15.1 and m = - 0.14 into y = mx + c. It becomes

    15.1 = - 0.14 * 35 + c

    15.1 = - 4.9 + c

    c = 15.1 + 4.9

    c = 20

    The linear function becomes

    y = - 0.14x + 20

    The remaining credit after 94 minutes of calls would be

    y = - 0.14 * 94 + 20

    y = - 13.16 + 20

    y = $6.84
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