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Ram rows a boat against a stream flowing at 2 km/h for a distance of 1
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25 Apr 2021, 11:50
25 Apr 2021, 11:50
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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
(A) 5 km/h
(B) 4 km/h
(C) 3 km/h
(D) 2 km/h
(E) 1 km/h
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Re: Ram rows a boat against a stream flowing at 2 km/h for a distance of 1
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25 Apr 2021, 11:57
25 Apr 2021, 11:57
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Carcass wrote:
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
(A) 5 km/h
(B) 4 km/h
(C) 3 km/h
(D) 2 km/h
(E) 1 km/h
Let's start with the word equation
Since the total travel time is 8 hours, we can write: (travel time upstream) + (travel time downstream) = 8 hours
Let x = Ram's rowing speed.
So, Ram's net speed travelling upstream = x - 2 (since the stream moves against him at 2 km/h)
Conversely, Ram's net speed travelling downstream = x + 2 (since the stream moves with him at 2 km/h)
Time = distance/net speed
We can now substitute into our word equation to get: 12/(x-2) + 12/(x+2) = 8 hours
ASIDE: At this point, we can either plug the five answer choices into our equation above, or we can solve the equation.
Since solving the equation will result in solving a quadratic equation, I think the fastest option is to test answer choices.
A) If x = 5, then we get: 12/(5-2) + 12/(5+2) = 8
Simplify: 12/3 + 12/7 = 8 hours
Doesn't work.
B) If x = 4, then we get: 12/(4-2) + 12/(4+2) = 8
Simplify: 12/2 + 12/6 = 8
Works!!
Answer: B
gmatclubot
Re: Ram rows a boat against a stream flowing at 2 km/h for a distance of 1 [#permalink]
25 Apr 2021, 11:57
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