Math

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If a light bulb that burns 3 hours a day lasts for 22.8 years, then how long will a light bulb that burns for 7 hours a day last?

  • Math -

    (3/7)(22.8) =

  • Math -

    burnhours of the lightbulb = 3(22.8) = 68.4

    time for a bulb that burns 7 hours/day
    = 68.4/7 =9.77
    or 9.8 years

    or
    the time is inversely proportional to the rate
    T = k/R
    22.8 = k/3
    k = 3(22.8) = 68.4
    T = 67.4/R
    = 67.4/7 = appr 9.8

    Notice the calculations are the same

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