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college math

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It takes Mike 8 minutes to walk to the store from his house. The return trip takes 13 minutes because he walks 1mph slower due to the bags he is carrying. How fast did Mike walk on his way to the store? Carry out one decimal place.
Thanks in advance!

  • college math -

    rate going to store --- x mph
    rate coming back ----- x-1 mph

    (8/60)x = (13/60)(x-1)
    times 60
    8x = 13(x-1)
    8x - 13x = -13
    -5x = -13
    x = 2.6

    So he walked to the store at 2.6 mph

    (8/60)(2.6) = .34666...
    (13/60)(1.6) = .34666... , ---> same distance

  • college math -

    distance = speed*time, and the two distances are the same, so

    8s = 13(s-1)
    s = 13/5 = 2.6 mph

    Note that we can mix minutes and mph, because the same factor would be applied to both sides if we converted everything to minutes or hours. As long as the units on both sides match, we are ok.

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