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Two trains are heading toward each other on a 750-kilometer straight

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Two trains are heading toward each other on a 750-kilometer straight [#permalink]

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New post 28 Mar 2017, 01:51
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Two trains are heading toward each other on a 750-kilometer straight track. One train is heading due east at 70 kilometers per hour and the other train is heading due west at 80 kilometers per hour. How much time do the conductors have before the trains collide?

A. 3 hours
B. 4 hours
C. 5 hours
D. 9 hours
E. 11 hours
[Reveal] Spoiler: OA

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Re: Two trains are heading toward each other on a 750-kilometer straight [#permalink]

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New post 28 Mar 2017, 02:03
its a head on collision,,, so time taken to collide = 750 / (80+70) = 5 hrs

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Re: Two trains are heading toward each other on a 750-kilometer straight [#permalink]

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New post 28 Mar 2017, 02:05
Both train will collide after 750/80+70= 5 hours later , so option c should be the answer

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Two trains are heading toward each other on a 750-kilometer straight [#permalink]

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Re: Two trains are heading toward each other on a 750-kilometer straight [#permalink]

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New post 30 Mar 2017, 15:40
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Bunuel wrote:
Two trains are heading toward each other on a 750-kilometer straight track. One train is heading due east at 70 kilometers per hour and the other train is heading due west at 80 kilometers per hour. How much time do the conductors have before the trains collide?

A. 3 hours
B. 4 hours
C. 5 hours
D. 9 hours
E. 11 hours


Since the trains are heading toward each other, we can let the time when the two trains would meet be t. Since distance = rate x time, the distance of the train heading east is 70t and the distance of the train heading west is 80t.

Now we can determine t:

distance of 1st train + distance of 2nd train = total distance

70t + 80t = 750

150t = 750

t = 5 hours

Alternate Answer:

Since one train travels 70 km an hour and the other travels 80 km an hour, the distance between the trains decreases 70 + 80 = 150 km every hour. Since they were 750 km apart, there will be 750/150 = 5 hours for the conductors to stop them before they collide.

Answer: C
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Re: Two trains are heading toward each other on a 750-kilometer straight [#permalink]

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New post 21 Apr 2017, 22:18
Option: C
Time Taken: 0:48
add the two speeds
150t=750
t=750/150
t=5 hours
after this time they will collide
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Re: Two trains are heading toward each other on a 750-kilometer straight   [#permalink] 21 Apr 2017, 22:18
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