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A person can row a distance of 2 km upstream in 15min and downstream

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Bunuel
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A person can row a distance of 2 km upstream in 15min and downstream [#permalink] New post   02 Feb 2021, 07:00
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45% (medium)

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68% (02:01) correct 32% (02:22) wrong based on 73 sessions
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A person can row a distance of 2 km upstream in 15min and downstream in 6 min. What is the speed of the stream ?

(A) 7 km/h
(B) 6 km/h
(C) 5.6 km/h
(D) 4.5 km/h
(E) 4 km/h
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Re: A person can row a distance of 2 km upstream in 15min and downstream [#permalink] New post   02 Feb 2021, 07:07
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Let v be the speed of the boat in the constant water and x be the speed of the stream.

2/(v-x)=1/4
v-x=8

2/(v+x)=1/10
v+x=20

2x=12
x=6 B)
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Re: A person can row a distance of 2 km upstream in 15min and downstream [#permalink] New post   13 Feb 2021, 07:16
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Bunuel wrote:
A person can row a distance of 2 km upstream in 15min and downstream in 6 min. What is the speed of the stream ?

(A) 7 km/h
(B) 6 km/h
(C) 5.6 km/h
(D) 4.5 km/h
(E) 4 km/h

Solution:

We can let r = the speed (in km/h) of the boat in still water and s = the speed (in km/h) of the stream and create the equations:

(r - s) x 15/60 = 2

and

(r + s) x 6/60 = 2

Simplifying, we have:

r - s = 8 → Eq. (1)

and

r + s = 20 → Eq. (2)

Subtracting Eq. (1) from Eq. (2), we have:

2s = 12

s = 6

Answer: B
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A person can row a distance of 2 km upstream in 15min and downstream [#permalink] New post   18 Jan 2024, 09:03
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Bunuel wrote:
A person can row a distance of 2 km upstream in 15min and downstream in 6 min. What is the speed of the stream ?

(A) 7 km/h
(B) 6 km/h
(C) 5.6 km/h
(D) 4.5 km/h
(E) 4 km/h

\(S_u = 2*\frac{15}{60} = 2*4 = 8\) \({S_u = s - c}\)
\(S_d = 2*\frac{6}{60} = 2*10 = 20\) \({S_d = s + c}\)

Thus,\(S_d + S_u = 2s\) Thus, \(2s = 28\) , \(S = 14\)

So, \(c = 20 - 14 => 6\), Answer must be (B)
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gmatclubot
A person can row a distance of 2 km upstream in 15min and downstream [#permalink]
18 Jan 2024, 09:03
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