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a motorboat, which can travel at 20 miles per hour in still water, takes 3/5 as long to travel downstream on a river from a to b, as to return. Find the rate of the rivers current.

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2 answers
  1. speed of current --- x mph
    distance ---- d miles

    time to go downstream = d/(20+x)
    time to go upstream = d/(20-x)

    d/(20+x) = (3/5)d /(20-x)
    divide both sides by d
    1/(20+x) = 3/(5(20-x))
    cross-multiply
    60+3x = 100 - 5x
    8x = 40
    x = 5

    the speed of the current is 5 mph

    check:
    suppose the distance is 100 miles
    time to go downstream = 100/25 hrs = 4 hrs
    time to go upstream = 100/15 = 20/3 hrs or
    and (3/5)(20/3) = 4

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  2. Wow I wish I really understood this it sounds very interesting I wish I knew what y'all were talking about I wish some body would sit and explain it to me step by step but that will probably never happen

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