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A crew can row a certain course up the stream in 84 minutes; they can

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Intern
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Joined: 17 May 2011
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A crew can row a certain course up the stream in 84 minutes; they can  [#permalink]

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New post 21 May 2011, 05:25
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Difficulty:

  65% (hard)

Question Stats:

70% (02:40) correct 30% (02:33) wrong based on 20 sessions

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A crew can row a certain course up the stream in 84 minutes; they can row the same course down stream in 9 minutes less than they can row it in still water. How long would they take to row down with the stream

A. 45 or 23 minutes
B. 63 or 12 minutes
C. 60 minutes
D. 19 minutes
E. 25 minutes
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Re: A crew can row a certain course up the stream in 84 minutes; they can  [#permalink]

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New post 21 May 2011, 08:26
This did not seem to be an OG problem, so I searched and found the following :

http://www.urch.com/forums/gmat-problem ... tream.html

@ramkryp, please quote the source correctly while posting the problems.
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Re: A crew can row a certain course up the stream in 84 minutes; they can  [#permalink]

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New post 21 May 2011, 09:46
http://www.beatthegmat.com/boat-downstream-t54016.html

A method has been discussed here to nullify the calculations though.

All I can input here is,

speed of a crew in still water = 1/2 ( speed upstream + speed downstream)

approximating this for time,

t = 1/2(84+ (t-9))

giving t = 66 close to B. :)
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Re: A crew can row a certain course up the stream in 84 minutes; they can  [#permalink]

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New post 22 May 2011, 04:59
@ Subash, I am sorry, I am new here.
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A crew can row a certain course up the stream in 84 minutes; they can  [#permalink]

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New post 25 Apr 2018, 22:09
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ramkryp wrote:
A crew can row a certain course up the stream in 84 minutes; they can row the same course down stream in 9 minutes less than they can row it in still water. How long would they take to row down with the stream

A. 45 or 23 minutes
B. 63 or 12 minutes
C. 60 minutes
D. 19 minutes
E. 25 minutes


let r=rowing speed
c=current speed
t=downstream time
1=distance
r+c=1/t
r-c=1/84
adding, 2r=1/t+1/84
r=1/(t+9)
thus, (1/t+1/84)/2=1/(t+9)
➡t^2-75t+756=0
(t-63)(t-12)=0
t=63 or 12 minutes
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A crew can row a certain course up the stream in 84 minutes; they can &nbs [#permalink] 25 Apr 2018, 22:09
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A crew can row a certain course up the stream in 84 minutes; they can

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