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# In a stream with a current of 5 kilometers per hour a boat

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Manager
Joined: 25 Feb 2008
Posts: 54
Followers: 0

Kudos [?]: 8 [0], given: 0

In a stream with a current of 5 kilometers per hour a boat [#permalink]  21 Mar 2008, 05:18
In a stream with a current of 5 kilometers per hour a boat made a trip downstream from point A to a point B and then back upstream from point B to point A. Measured in still water, the boat’s average speed for the trip was 15 kilometers per hour. Measured in the stream, what was the boat’s average speed for the trip in kilometers per hour?
16 2/3
15
14 ½
13 1/3
13
Optional: time you spend on this question
Manager
Joined: 20 Aug 2007
Posts: 65
Followers: 1

Kudos [?]: 9 [1] , given: 0

Re: boat in the river [#permalink]  21 Mar 2008, 05:50
1
KUDOS
Capthan wrote:
In a stream with a current of 5 kilometers per hour a boat made a trip downstream from point A to a point B and then back upstream from point B to point A. Measured in still water, the boat’s average speed for the trip was 15 kilometers per hour. Measured in the stream, what was the boat’s average speed for the trip in kilometers per hour?
16 2/3
15
14 ½
13 1/3
13
Optional: time you spend on this question

Let distance from A to B = S
downstream speed = 15+5=20 .... time used = S/20
upstream speed = 15-5=10 .... time used = S/10

average speed = total distance/total time spend
=2S / (3S/20)
= 40/3
= 13 1/3

edit for typo
Re: boat in the river   [#permalink] 21 Mar 2008, 05:50
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