Anonymous
Anonymous asked in Science & MathematicsMathematics · 9 years ago

Math questions? Quadratic Word Problem? Please help?

It took a crew 80 min to row 3 km upstream and back again. If the rate of folow of the stream was 3 km/h, what was the rowing rate of the crew?

Please clarify by showing all work. Thanks.

2 Answers

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  • Ossi G
    Lv 7
    9 years ago
    Favorite Answer

    Hello

    let v = velocity of the crew.

    and time = distance/velocity : t = s/v

    time to go upstream = t1 = 3/(v-3)

    time to go downstream = t2 = 3/(v+3)

    together : t1 + t2 = 80/60 h = 8/6 h

    3/(v-3) + 3/(v+3) = 8/6

    ((v+3) + (v-3))/(v^2 - 9) = 8/6

    36v = 8v^2 - 72

    v^2 - 4.5v - 9 = 0

    v = 2.25 +- √(2.25^2 + 9)

    v = 2.25 +- 3.75

    v = 6 km/h <--- ans.

    Regards

  • Erika
    Lv 4
    4 years ago

    Vertex = (4, 250) 2d aspect = (9,0) Vertex variety: h - 250 = a(d - 4)^2 plug in (9,0) for (d,h) -250 = a(9-4)^2 -250 = 25a a = -250÷ 25 = -10 so h - 250 = -10(d - 4)^2 h(d) = -10(d - 4)^2 + 250

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