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# Two trains, which are 600 miles apart, are heading toward each other o

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Math Expert
Joined: 02 Sep 2009
Posts: 64168
Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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14 Mar 2017, 22:09
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87% (00:56) correct 13% (01:53) wrong based on 101 sessions

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Two trains, which are 600 miles apart, are heading toward each other on a straight track. One train is heading due east at 70 miles per hour and the other is heading due west at 80 miles per hour. How much time do the conductors have to stop the trains before they collide (assuming the trains can be stopped instantaneously)?

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

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Re: Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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20 Mar 2017, 05:46
1
Bunuel wrote:
Two trains, which are 600 miles apart, are heading toward each other on a straight track. One train is heading due east at 70 miles per hour and the other is heading due west at 80 miles per hour. How much time do the conductors have to stop the trains before they collide (assuming the trains can be stopped instantaneously)?

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

Sine 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 = 600

150t = 600

t = 4 hours

Since one train travels 70 miles and the other travels 80 miles every hour, the distance between the trains decreases 70 + 80 = 150 miles every hour. Since they were 600 miles apart, there will be 600 / 150 = 4 hours for the conductors to stop them before they collide.

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Re: Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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14 Mar 2017, 22:26
total speed is :- 150 mph
distance is 600 m

time = 600/150 = 4 hours

conductors have 3 hours to stop as in 4 th hour they will collide...hence A
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Re: Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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14 Mar 2017, 22:49
as per the solution mentioned above,
total speed is :- 150 mph
distance is 600 m

time = 600/150 = 4 hours

conductors have 3 hours to stop as in 4 th hour they will collide...hence A

the time calculated as 4 hours is correct, making B as correct answer choice. As mentioned in the question, the train can be stopped instantaneously, no time will be required to stop the train and hence 4 is the time required.
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Re: Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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14 Mar 2017, 23:05

(assuming the trains can be stopped instantaneously)
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Re: Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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14 Mar 2017, 23:26
the trains are on a head on collision

ans B
4 hours...
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Re: Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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18 Mar 2017, 19:18

We have to find ,after departure, at what time they will collide each other

In one hour, Both Trains will cover = 70+ 80 miles = 150 miles.
They will collide with each other in = 600/150 miles = 4 Hours.

As trains can be stopped instantaneously,Conductor can have to respond 4 Hours time to prevent the collision of trains.
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Re: Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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26 Jun 2019, 23:17
Bunuel wrote:
Two trains, which are 600 miles apart, are heading toward each other on a straight track. One train is heading due east at 70 miles per hour and the other is heading due west at 80 miles per hour. How much time do the conductors have to stop the trains before they collide (assuming the trains can be stopped instantaneously)?

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

relative Speed: 150
Distance to cover: 600, so it'll take 4 hours to cover 600 miles travelling at a speed of 150 m/hr.
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Re: Two trains, which are 600 miles apart, are heading toward each other o  [#permalink]

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27 Jun 2019, 02:09
total distance is 600 miles and the sum of distance that first and second train covers is600. also time for both the trains s the same
hence, 70xT+80xT=600

t=4
Re: Two trains, which are 600 miles apart, are heading toward each other o   [#permalink] 27 Jun 2019, 02:09