A fish can swim 45 miles downriver in the same amount of time that it can swim 27 miles upriver.Find the speed?

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  • 8 years ago
    Favorite Answer

    x = speed of fish

    y = speed of current

    effective speed dwon river = x+y

    effective speed upriver = x - y

    rate * time = distance OR

    time = distance / rate

    time is the same, so set them equal to each other

    45/(x+y) = 27/(x-y)

    cross multiply

    45 (x-y) = 27 (x+y)

    you can play with that, but you will not get an actual answer (only a ratio of x and y since you did not specify the time)

    18x = 72y

    x = 4y

    swim speed is four times the current.

    NOTE: the swim speed is the midpoint between the upriver and the down river speed, but the problem does not say the time is an hour, it only says the time is the same.

  • DWRead
    Lv 7
    8 years ago

    Find the speed of what? the river or the fish in still water?

    r = speed of the river current

    f = speed of the fish in still water

    45/(f + r) = 27/(f - r)

    45(f - r) = 27(f + r)

    18f = 72r

    f = 4r

    The fish's speed is 4 times the speed of the current.

  • Ian H
    Lv 7
    8 years ago

    36 mph

    Because u is the average between (u + v) and (u - v)

    (45 + 27)/2 = 36

    Regards - Ian

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