A boat takes 3 hours to travel 30 km down a river, then 7 hours to return. How fast is the river flowing?

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  • EM
    Lv 7
    1 decade ago
    Favorite Answer

    (distance) = (speed)(time)

    30 km = (b + c)(3 hr)

    10 = b + c [1]

    30 km = (b - c)(7 hr)

    30/7 = b - c [2]

    [1] - [2]:

    10 - 30/7 = (b + c) - (b - c)

    40/7 = 2c

    c = 20/7 km/h ≈ 2.86 km/h

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