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anonymous

  • one year ago

A boat travels at a rate of 15km/hr in still water . It travels 60km upstream in the same time that it travels 90km downstream. What is the rate of the current ?

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  1. mathstudent55
    • one year ago
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    Current speed = c Boat speed is still water = s Boat speed upstream = s - c Boat speed downstream = s + c

  2. mathstudent55
    • one year ago
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    speed = distance/time

  3. mathstudent55
    • one year ago
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    distance = speed * time

  4. mathstudent55
    • one year ago
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    You understand the table so far? |dw:1435634606883:dw|

  5. anonymous
    • one year ago
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    Mk but we don't know the time

  6. anonymous
    • one year ago
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    Ya I get the table

  7. mathstudent55
    • one year ago
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    |dw:1435634823006:dw|

  8. mathstudent55
    • one year ago
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    Using: distance = speed * time you get this system of equations: 60 = (15 - c)t 90 = (15 + c)t

  9. mathstudent55
    • one year ago
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    We solve both equation for t and set them equal to each other: \(t = \dfrac{60}{15 - c} \) \(t = \dfrac{90}{15 + c} \)

  10. mathstudent55
    • one year ago
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    \(\dfrac{60}{15 - c} = \dfrac{90}{15 + c} \)

  11. mathstudent55
    • one year ago
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    Cross multiply: 90(15 - c) = 60(15 + c) Divide both sides by 10: 9(15 - c) = 6(15 + c) 135 - 9c = 90 + 6c -15c = -45 c = 3

  12. mathstudent55
    • one year ago
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    The current is 3 km/h

  13. anonymous
    • one year ago
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    Okay I understand it I have 3 more problems like this but can u tell me if I am doing it right ?

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