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Marah
Lv 5
Marah asked in Science & MathematicsMathematics · 10 years ago

Speed/Rate World Problem?

Alvin paddeled for 5 hours with a 4-km/h current to reach a campsite. The return trip against the same current took 9 hours. What is the speed of the boat in still water?

Update:

I'm more interested in how to set up the problem then the particular answer. If anyone could show their work (with or without the answer), that would be great. Thank you!

1 Answer

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  • ranjankar
    Lv 7
    10 years ago
    Favorite Answer

    LET THE SPEED OF BOAT IN STILL WATERS BE X KM / HOUR

    SPEED OF CURRENT = 4 KM / HOUR

    DISTANCE TRAVELED = SPEED X TIME

    DOWNSTREAM SPEED = ( X + 4) KM / HOUR

    UPSTREAM SPEED = ( X -4) KM / HOUR

    SINCE THE DISTANCE TRAVELED EACH WAY IS THE SAME , WE GET THE EQUATION

    5 ( X+4) = 9 ( X -4)

    5X +20 = 9X -36

    4X = 56

    X = 14 KM/ HOUR ANSWER

    CHECK

    5 x ( 14+4) = 90 KM

    9 x ( 14-4) = 90 KM

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