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Ram rows a boat against a stream flowing at 2 km/h for a distance of [#permalink]
Quote:
Ram rows a boat against a stream flowing at 2 km/h for a distance of 12 km and then turns around and rows back with the current. If the whole trip lasts 8hours, find Ram’s rowing speed in still water.

(A) 5 km/h
(B) 4 km/h
(C) 3 km/h
(D) 2 km/h
(E) 1 km/h


Let Ram's rowing speed in still water be 'S'
Then, Speed while rowing upstream against the flow = (S-2)
&, Speed while rowing DOWNSTREAM with the flow =(S+2)
Asper ques, Total time taken = 8 hrs
Time taken rowing upstream for 12 km = 12/ (S-2)
& Time taken rowing downstream for 12 km = 12/(S+2)

Therefore, 12/ (S-2) + 12/(S+2) = 8
Taking LCM & Solving
12S+24 +12S-24 / (S-2)(S+2) =8
24S = 8(S^2 -4)
S^2 -3S-4 =0
(S-4)(S+1) = 0
S= -1 or +4
Since speed cannot be negative, Discarding -1
Hence, Speed in still water = 4 km/h
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Re: Ram rows a boat against a stream flowing at 2 km/h for a distance of [#permalink]
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Re: Ram rows a boat against a stream flowing at 2 km/h for a distance of [#permalink]
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