college algebra word problem?

A Mississippi riverboat can travel 70 kilometers downstream in 5 hours and can make the return trip in 7 hours. Find the speed of the boat in still water.

2 Answers

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  • 8 years ago
    Favorite Answer

    Let speed of boat in still waters be x km / hour and speed of current be y km/ hour

    DOWNSTREAM

    -------------------------

    SPEED = DISTANCE / TIME

    ( x+ y ) = 70/5 = 14 .............(A)

    UPSTREAM

    --------------------

    SPEED = DISTANCE / TIME

    x - y = 70/7 = 10 ..............(B)

    (A) + (B)

    2x = 24

    x = 12km/ hour ANSWER

    y = 2 km/ hour

    CHECK

    DOWNSTREAM = 70 / (12+2) = 5 hours

    UPSTREAM = 70 / (12-2) = 7 hours

  • David
    Lv 7
    8 years ago

    let

    x = speed of the boat

    y = speed of the river

    5(x + y) = 70

    x + y = 14

    7(x - y) = 70

    x - y = 10

    x + y = 14

    x - y = 10

    2x = 24

    x = 12 kph

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