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# A swimmer practiced in a still water inlet a river made in

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Current Student
Joined: 11 May 2008
Posts: 552
A swimmer practiced in a still water inlet a river made in [#permalink]

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09 Sep 2008, 21:46
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

A swimmer practiced in a still water inlet a river made in its bank, and achieved a speed of 4 km/h. When she was swimming upstream in the river, however, she could only make 3 km/h. One day the swimmer swam into the river from the inlet, then doubled the covered distance going downstream, and finally came back. She averaged 3.8 km/h that day. What was her downstream speed?

* 4
* 5
* 6
* 7
* 8

we can find out downstream speed in just two steps..
i think all the other information is not reqd..
what do you people think?
SVP
Joined: 17 Jun 2008
Posts: 1507
Re: up stream and downstream [#permalink]

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09 Sep 2008, 23:43
arjtryarjtry wrote:
A swimmer practiced in a still water inlet a river made in its bank, and achieved a speed of 4 km/h. When she was swimming upstream in the river, however, she could only make 3 km/h. One day the swimmer swam into the river from the inlet, then doubled the covered distance going downstream, and finally came back. She averaged 3.8 km/h that day. What was her downstream speed?

* 4
* 5
* 6
* 7
* 8

we can find out downstream speed in just two steps..
i think all the other information is not reqd..
what do you people think?

I also got 5 kmph. However, I am not able to get how 3.8 kmph will be the average speed in the second case.

Calling math gurus for help.
Senior Manager
Joined: 31 Jul 2008
Posts: 281
Re: up stream and downstream [#permalink]

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10 Sep 2008, 14:08
hmm .. there is a catch i think

from the first set of info we can deduce the speed of the stream. i.e 1 km/hr

now in the second case there is no reason to believe that the swimmer swam with the same speed as he had on the previous occasion.

so then we need to deduce the speed

3.8 = 2d / [d/(s+1) + d/(s-1)] where d= distance travelled and s=swimmer's speed
Retired Moderator
Joined: 18 Jul 2008
Posts: 921
Re: up stream and downstream [#permalink]

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10 Sep 2008, 15:41
So apparently you need physics to solve this problem under 2 minutes

Re: up stream and downstream   [#permalink] 10 Sep 2008, 15:41
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# A swimmer practiced in a still water inlet a river made in

Moderator: chetan2u

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