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M03 Q 36

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A swimmer makes a round trip up and down the river. It takes [#permalink] New post 12 Oct 2008, 14:56
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A swimmer makes a round trip up and down the river. It takes him X hours. The next day he swims the same distance with the same speed in the still water. It takes him Y hours. What can we say about X and Y ?

(C) 2008 GMAT Club - m03#36

* X > Y
* X < Y
* X = Y
* X = \frac{1}{2}Y
* none of the abov

I felt that this Q leaves a lot to imagine/assume. I find this very atypical of GMAT

Thanks
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Re: M03 Q 36 from GMAT Club [#permalink] New post 12 Oct 2008, 15:27
I solve it this way:

If c is the water speed, v the swimmer speed, d the length of the river, then we have:

d/(v+c) + d/(v-c) = X
and
2d/v=Y

X/d = 1/(v+c) + 1/(v-c) = 2v / ((v+c)(v-c)) = 2v / (v^2-c^2) > 2/v = Y/d

i.e. X>Y

Answer is then A.
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Re: M03 Q 36 from GMAT Club [#permalink] New post 12 Oct 2008, 15:30
Lets assume that the speed of the person = 10Miles/Hr
Assume that total the distance of up and down of the river the person swam = 10 Miles
Assume the downward speed of the river stream = 2 Miles/Hr

Now Time taken by the person to cover upstream end of the river which is half of total distance,
using formula (Time = Distance / Speed)
= (Half of distance of river) / (Speed of person + speed of river current)
= 5 / (10 + 2) = 5/12
Similarly Time taken to swim the downstream = (Half of distance of river) / (Speed of person - speed of river current)
= 5/(10 - 2) = 5/8
Total time = 5/12 + 5/8 = 25/24 > 1
Now to swim in still water to cover the same distance with same speed, Time taken = 10 / 10 = 1

So I think, the answer is X > Y. Please let me know if there is a better way to solve this.

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Re: M03 Q 36 from GMAT Club [#permalink] New post 13 Oct 2008, 18:10
IMO A: x >y

* when you have only 1 or 2 min.left in exam
Y hours taken in STILL water.. so it is obvious it will take less time .there is no resistence while upstream and no force while downstream

X hours takes in normal water..so there is some resistence... so X is greater than Y.

* when you have good amount of time

River : 100km/h
ManSpeed: 3 km/h
RiverSpeed:2km/h

Case 1:X = 100/1+100/5 = 100+20 =120 hours

Case 2:Y = 100/3+100/3 = 33.33+33.33=67 hours

x > y :)

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Re: M03 Q 36 from GMAT Club [#permalink] New post 14 Oct 2008, 07:59
Y hours taken in STILL water.. so it is obvious it will take less time .there is no resistence while upstream and no force while downstream

X hours takes in normal water..so there is some resistence... so X is greater than Y.


..indeed is the most logical way to imagine it
and makes the question much easier than earlier thought
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Re: M03 Q 36 from GMAT Club [#permalink] New post 06 Nov 2008, 14:43
icandy wrote:
A swimmer makes a round trip up and down the river. It takes him X hours. The next day he swims the same distance with the same speed in the still water. It takes him Y hours. What can we say about X and Y ?

(C) 2008 GMAT Club - m03#36

* X > Y
* X < Y
* X = Y
* X = \frac{1}{2}Y
* none of the abov

I felt that this Q leaves a lot to imagine/assume. I find this very atypical of GMAT

Thanks


I agree with icandy, the data is not sufficient

What if the swimmer was tired the next day :wink:
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Re: M03 Q 36 from GMAT Club [#permalink] New post 13 Nov 2008, 11:50
I agree that this question leaves too much up to the imagination, which is not what you're supposed to do on the GMAT.

It's quite possible that X = Y. The question doesn't state that the swimmer didn't swim in still water on day one. We can certainly assume that there was a current in the water, but I expected that to be the trap (to assume). T=D/R and he swam at the same R for the same D, therefore it could be the same T. It's not specified whether the swimmers speed is his overall speed or speed without resistance.

Any of the following are defensible answers:
X>Y (with assumptions)
X=Y (without assumptions)
None of the above. (too ambiguous to answer)

Overall, I dislike this question :)
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Re: M03 Q 36 from GMAT Club [#permalink] New post 14 Nov 2008, 15:55
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The way I thought of this was to imagine the speed of the river going upstream to be greater than the speed of the swimmer; the time will be infinite as the swimmer will never be able to reach any point upstream.
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Confusing Questions [#permalink] New post 07 Aug 2009, 19:46
A swimmer makes a round trip up and down the river which takes her x hours. If the next day she swims the same distance with the same speed in still water, which takes x her hours, which of the following statements is true?

x>y
x<y
x=y
x=1/2Y
none of the above

I chose E here because the question does not talk about currents. Based on my experience GMAT does not allow assumptions with questions. Please clarify.

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Re: Confusing Questions [#permalink] New post 08 Aug 2009, 03:55
Expert's post
Please follow the guidelines of posting in this forum; otherwise we are not able to offer support
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Re: Confusing Questions [#permalink] New post 08 Aug 2009, 20:01
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I apologize bb for not following the rules. I am referring to exam 3 question 36. I read through the discussion but was not convinced. I thought the question asked us to assume more than an actual GMAT would.

What are your thoughts?
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M03 Q 36 [#permalink] New post 08 Aug 2009, 21:17
Expert's post
sher676 wrote:
I apologize bb for not following the rules. I am referring to exam 3 question 36. I read through the discussion but was not convinced. I thought the question asked us to assume more than an actual GMAT would.

What are your thoughts?


I have merged the threads - no reason to have 2 about the same topic.

Sure - it sounds that several people felt the question was open ended. Kudos for the feedback. I have missed the previous thread.
Happy to adjust the question. Please advise if I understand it correctly - Is the main issue with the current up and down the river?

What do you think if I rephrased the question to be "John swam from point A to point B against the river current and then immediately swam from point B back to point A with the current. If the following day he swam twice the distance from point A to point B but in still water, what can we say about X and Y?"
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Re: M03 Q 36 [#permalink] New post 21 Aug 2009, 02:38
We are not given the upstream and downstream speeds, if upstream=downstream then X=Y else we have all possibilities!
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Re: M03 Q 36 [#permalink] New post 21 Aug 2009, 10:58
The answer should be A, X>Y

suppose the speed of the swimmer is R, and the speed of the river is r, it took the swimmer X1 hours from upstream to downstream, X2 hours from downstream to upstream.

the hidden information here is R>r

we can get the equation as below:
1) (R+r)X1+(R-r)X2=RY
2) (R+r)X1=(R-r)X2
3) X1+X2=X

from 2) and 3), we get (R+r)X1=(R-r)(X-X1)
4) X1= (R-r)X/2R

from 1) 2) 4), we get 2(R^2-r^2)X/2R=RY
(R^2-r^2)*X=R^2*Y

Therefore the answer is X>Y
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Re: M03 Q 36 [#permalink] New post 29 Oct 2009, 11:26
I agree with the above discussion. The problem is that the swimmer could be travelling in still water both days. We can't assume that the current is present on day 1.

I think the question could be worded as follows.

If the next day she swims the same distance with the same speed in still water, which takes her hours, which of the following statements MUST BE true?

Answer choice could be

X >= Y - this solves the issue with the currents being equal and still tests having to solve the equation.
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Re: M03 Q 36 [#permalink] New post 30 Sep 2010, 19:32
I took this test today and was on a roll until I got to this question. Wasn't sure what I was supposed to do and it seemed like not enough info was given. If there was something about the amount of resistance when swimming upstream it would have helped. Doesn't seem like a question that would be on the actual GMAT so I just guessed and moved on.
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Re: M03 Q 36 [#permalink] New post 17 Oct 2010, 17:50
u-v, u, u+v are speeds upstream, still water and downstream respectively.

Let the corresponding time taken are a,b,c

Also 2b=Y and a+c = X --> given.

When speeds are in AP the time taken are in HP.
=> b = \frac{2ac}{(a+c)}

Also AM > HM => \frac{(a+c)}{2} > \frac{2ac}{(a+c)}

=> X> \frac{4ac}{(a+c)}

=> X > 2b

=> X > Y
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Re: M03 Q 36 from GMAT Club [#permalink] New post 17 Oct 2010, 17:54
Avernusaur wrote:
I agree that this question leaves too much up to the imagination, which is not what you're supposed to do on the GMAT.

It's quite possible that X = Y. The question doesn't state that the swimmer didn't swim in still water on day one. We can certainly assume that there was a current in the water, but I expected that to be the trap (to assume). T=D/R and he swam at the same R for the same D, therefore it could be the same T. It's not specified whether the swimmers speed is his overall speed or speed without resistance.

Any of the following are defensible answers:
X>Y (with assumptions)
X=Y (without assumptions)
None of the above. (too ambiguous to answer)

Overall, I dislike this question :)


How can someone swim upstream and downstream without considering the speed of the river?
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Re: M03 Q 36 [#permalink] New post 27 Feb 2011, 10:57
The question does not say whether the swimmer swims with the water current or against it
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Re: M03 Q 36 [#permalink] New post 02 May 2011, 12:44
achellappa wrote:
The question does not say whether the swimmer swims with the water current or against it


as it's a round trip, it doesn't matter as the swimmer will swim one half of the journey with the current, and the other half against it...

Logically X>Y (assuming a river flows), though slight confusion is raised by the question as it states the swimmer covers the same distance at the same speed on the second day. As 'speed' is not further qualified and "speed = distance/time", one could be easily forgiven to say X=Y.

Additional information would probably be provided on the test, but otherwise this is quite a nice mental exercise to get you thinking :) :)
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Re: M03 Q 36   [#permalink] 02 May 2011, 12:44
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