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Two trains are headed along parallel tracks in the same direction at

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Two trains are headed along parallel tracks in the same direction at [#permalink]

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New post 28 Jul 2017, 08:35
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Two trains are headed along parallel tracks in the same direction at varying rates of 72 mph and 47 mph. In how many hours will the faster train be 100 miles in front of the slower train?

(A) 2

(B) 2.5

(C) 3.5

(D) 4

(E) Cannot be determined by information provided.
[Reveal] Spoiler: OA

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Re: Two trains are headed along parallel tracks in the same direction at [#permalink]

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New post 28 Jul 2017, 12:16
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Since the trains are travelling in the same direction, the relative speed is x1 - x2
if x1 and x2 are the speeds of both the trains.

Given data : x1 = 72mph, x2 = 47 mph
Relative speed = 72-47 = 25mph

To get 100 miles ahead, both the trains would have to travel 4 hours.(Option D)
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Re: Two trains are headed along parallel tracks in the same direction at [#permalink]

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New post 29 Jul 2017, 09:27
D=R*T

Distance traveled of Train 1 after T hours is 72*T
Distance traveled of Train 2 after T hours is 27*T
After T hours, Train 1 has gained 100 miles more: 72T-27T = 100 --> T=4

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Re: Two trains are headed along parallel tracks in the same direction at [#permalink]

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New post 29 Jul 2017, 11:46
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Answer cannot be determined as we don't know initial positions of trains relative to each other. Answers posted would work if both the trains started from the same point and at the same time. Hence E

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Re: Two trains are headed along parallel tracks in the same direction at [#permalink]

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New post 29 Jul 2017, 18:46
rhtmhjn wrote:
Answer cannot be determined as we don't know initial positions of trains relative to each other. Answers posted would work if both the trains started from the same point and at the same time. Hence E

Thought the same, however answered D..will wait for the formal response.

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Re: Two trains are headed along parallel tracks in the same direction at [#permalink]

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New post 06 Sep 2017, 04:57
Bunuel wrote:
Two trains are headed along parallel tracks in the same direction at varying rates of 72 mph and 47 mph. In how many hours will the faster train be 100 miles in front of the slower train?

(A) 2

(B) 2.5

(C) 3.5

(D) 4

(E) Cannot be determined by information provided.


As the realtive speed is 25mph. In an hr the fast train will be 25 miles ahead. So to cover 100 miles the fast train needs 4 hrs.

Ans:D

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Re: Two trains are headed along parallel tracks in the same direction at [#permalink]

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New post 11 Sep 2017, 10:57
Bunuel wrote:
Two trains are headed along parallel tracks in the same direction at varying rates of 72 mph and 47 mph. In how many hours will the faster train be 100 miles in front of the slower train?

(A) 2

(B) 2.5

(C) 3.5

(D) 4

(E) Cannot be determined by information provided.


Let t = the time in hours the two trains have traveled when the faster train is 100 miles ahead of the slower train. So, the distances traveled by the faster train and slower train are 72t and 47t, respectively, and we can create the following equation:

72t = 47t + 100

25t = 100

t = 4

Answer: D
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Re: Two trains are headed along parallel tracks in the same direction at   [#permalink] 11 Sep 2017, 10:57
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