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greatuser

it took 2hrs

  • 9 months ago
  • 9 months ago

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  1. greatuser
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    it took 2hrs for boat to go from a to b with current and 6hrs to go back against curent. assuming constant speed of boat in both directions, how long wil it take raft (with speed equal to speed of curent) to go from a to b?

    • 9 months ago
  2. hartnn
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    let the boat (without any current) take 'x' hrs to reach from a to b and the raft (with speed equal to speed of current) take 'y' hrs to reach from a to b when current assist boat, total time taken was 2 hours, so x-y= 2 when current was against the boat, time taken was 6hrs , so x+y =6 find 'y' from here :)

    • 9 months ago
  3. greatuser
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    that means x=y+2=6-y which means y=2? that cant be right though

    • 9 months ago
  4. hartnn
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    yeah, i think i have overlooked something speed = distance / time here, distance is same so, speed * time will be constant let their speed be 'a' and 'b' so, (a+b)*2=(a-b)*6=distance =d and you need, time taken by raft, = d/b try it!

    • 9 months ago
  5. greatuser
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    but d and b are both unknown. how can we solve it?

    • 9 months ago
  6. greatuser
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    please help i still don't get it

    • 9 months ago
  7. greatuser
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    so far, a= speed of boat b = sped of current 6a-6b = 2a + 2b meaning a = 2b

    • 9 months ago
  8. dumbcow
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    "d" is an arbitrary distance that is constant for all trips....let d=1 then 1/(a+b) = 2 1/(a-b) = 6 a = 2b 1/3b = 2 1/b = 6 --> b = 1/6 --> d/b = 6 it would take raft 6 hours

    • 9 months ago
  9. greatuser
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    oh i get i now thanks a lot

    • 9 months ago
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