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A man can row at 5 km/h in still water. If the speed of the stream is

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Bunuel
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A man can row at 5 km/h in still water. If the speed of the stream is [#permalink] New post   08 Jun 2021, 09:00
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A man can row at 5 km/h in still water. If the speed of the stream is 1 km/h and it takes 1 h to row to a place and come back, how far is the place?

(A) 2.4 km
(B) 2.5 km
(C) 3 km
(D) 3.6 km
(E) 4.2 km
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AndreaBer
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A man can row at 5 km/h in still water. If the speed of the stream is [#permalink] New post   Updated on: 08 Jun 2021, 11:33
we know that the man can row at 5km/h and the speed of the stream is 1km/h.
this means that :

speed downstream: (5+1)= 6 km/h
speed upstream: (5-1)= 4km/h

so x/4 + x/6 = 1 hour

x= 2.4km

answer: A

Originally posted by AndreaBer on 08 Jun 2021, 09:49.
Last edited by AndreaBer on 08 Jun 2021, 11:33, edited 3 times in total.
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Re: A man can row at 5 km/h in still water. If the speed of the stream is [#permalink] New post   08 Jun 2021, 10:23
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AndreaBer wrote:
not sure, but let's try.

we know that the man can row at 5km/h and the speed of the stream is 1km/h. This means that the relative speed is 5+1= 6. Now, we know that it takes 6km/h * 1 hour ( Distance= speed*time) to row to a place and come back. Since the question asks for the distance of the place from the beginning we do not need to consider the way back. Thus, 6km/h * 0.5 = 3km

answer: C


the answer is 2.4km.

x/6+x/4=1

x=2.4
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Re: A man can row at 5 km/h in still water. If the speed of the stream is [#permalink] New post   08 Jun 2021, 23:29
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Solution:

We are given the speed of boat in still water = \(5 km/h\) and speed of stream \(1 km/h\)

It is said that the man 1 hour to row to the place and come back from there. Which he must have faced both upstream and downstream conditions once each.
Speed of the boat Upstream \(= 5-1=4km/h.\)
Speed of the boat Downstream \(= 5+1=6km/h \)

let the distance of the place be \(= x km\)

So, according to the problem: Time to go upstream + Time to go downstream = 1 hour.
\(⇒ \frac{x}{4}+\frac{x}{6}=1\)
\(⇒ \frac{6x+4x}{24}=1\)
\(⇒ 10x=24\)
\(⇒ x = 2.4 km. \)

Hence the right answer is Option A.
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Re: A man can row at 5 km/h in still water. If the speed of the stream is [#permalink] New post   09 Jun 2021, 04:11
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This is a question on the concept of Boats & Streams. In questions on boats & streams, the two cardinal equations to solve questions are:

    Effective speed of the boat downstream = Speed of boat in still water + speed of stream
    Effective speed of the boat upstream = Speed of boat in still water – speed of stream

Let us assume the place is d km away. Therefore,

\(\frac{d}{(5+1)}\) + \(\frac{d}{(5-1)}\) = 1.

Simplifying, we have \(\frac{d}{6} +\frac{ d}{4}\) = 1. Taking the LCM of the denominators and simplifying, we have,

\(\frac{2d + 3d }{ 12}\) = 1 OR

\(\frac{5d}{12}\) = 1

Therefore, d = \(\frac{12}{5}\) = 2.4 km.

The correct answer option is A.

Hope that helps!
Aravind B T
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Re: A man can row at 5 km/h in still water. If the speed of the stream is [#permalink] New post   07 May 2023, 17:07
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Re: A man can row at 5 km/h in still water. If the speed of the stream is [#permalink]
07 May 2023, 17:07
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