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Trains are leaving station A for station B every 15 minutes [#permalink]

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26 Aug 2008, 09:43

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Trains are leaving station A for station B every 15 minutes starting 8:00 am. The distance between the stations is 80 km. If a train leaves station B for station A at 11:05 am, how many oncoming trains will it meet?

1. Trains from station A to station B travel at 40 kmh 2. The train from station B to station A travels at 40 kmh

Trains are leaving station A for station B every 15 minutes starting 8:00 am. The distance between the stations is 80 km. If a train leaves station B for station A at 11:05 am, how many oncoming trains will it meet?

1. Trains from station A to station B travel at 40 kmh 2. The train from station B to station A travels at 40 kmh

I would go with C.

You need to know how many trains going from A to B are on the tracks 3 hours and 5 minutes after 8am. This requires you to know (1).

But that is not enough. You also need to know how many trains depart from station A in between 11:05 and the train's arrival at Station A. For this, you need to know how long the train takes to travel from B to A.

just a thought since u know the speed of train leaving from B to A, and teh distrance, u know how long it will travel so wont it just meet trains at 15 minute intervals irrespetive of how fast they travel?

do u really need the information of speed of train fro A to B?

You need to know speed of trains from A->B so that you can discard trains that have reached before 11.05 However this information alone is not sufficient as we need to know the speed of train from B->A. For example if this train is an express train traveling at 400km/h it would take less time to travel and hence meet fewer trains. However if this train is a slow coach traveling at 1km/hr it would meet a lot more trains. Both speeds are necessary.

Re: Trains are leaving station A for station B every 15 minutes [#permalink]

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29 May 2014, 02:51

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Re: Trains are leaving station A for station B every 15 minutes [#permalink]

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03 Jun 2014, 09:05

From (1) we get that train leaving from station A takes 2 hours to reach station B. But We are not given the speed of the trains leaving station B. Therefore Time taken for Train to reach from station A to B = ? . Not SUfficient From (2) it's Exactly the opposite of Option (1). Hence Not Sufficient

Combining (1) and(2) we get the Time taken by train to travel from each side and hence no of Oncoming trains can be calculated. Sufficient

P.S: Since this is a DS question we don't have to get the exact number

Hope This Helps
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Re: Trains are leaving station A for station B every 15 minutes [#permalink]

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03 Jul 2016, 08:43

16 is the answer .. Since train from station A which left left at 9 am reached st.B at 11 Therefore the train leaving leaving fr st.A at 9:15 will still be on its way to reaching St.B and will hit St.B at 11.15 in which it will encounter our train leaving St.B at 11 Therefore total trains crossing the train fr St B will be 16

Re: Trains are leaving station A for station B every 15 minutes [#permalink]

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13 Jan 2017, 16:44

Distance of 80 kms between the trains. We would need to know the speed of both the trains to calculate the time it would take for each train to reach the destination.

1)Trains from station A to station B travel at 40 kmh Each train takes D/T time to reach the destination. 80/40 km/h = 2 hours. So a train leaving station A at 8:00 am, would reach the destination at 10:00 pm. The other trains at 8:15,8:30, 8:45, 9:00 pm. However, we need to know the speed at which the train from station B travels to station A. This would determine the number of trains it would cross. No information on train B. Not Sufficient

2) The train from station B to station A travels at 40 kmh

Similar to the above case, we do not have any information on trains leaving from Station A. Hence, Not Sufficient.

Both together, we should be able to solve the problem. Below trains would travel from Station A - Station B. 8:00 - 10:00am 8:15 - 10:15 am 8:30 - 10:30 am 8:45 - 10:45 am 9:00 - 11:00 am 9:15 - 11:15 am 9:30 - 11:30 am. 9:45 - 11:45 am 10:00 - 12:00 pm 10:15 - 12:15 pm 10:30 - 12:30 pm 10:45 - 12:45 pm 11:00 - 1:00 pm 11:15 - 1:15 pm 11:30 - 1:30 pm 11:45 - 1:45 pm 12:00 - 2:00 pm 12:15 - 2:15 pm 12:30 - 2:30 pm 12:45 - 2:45 pm. 1:00 - 3:00 pm .

From Station B to Station A, starting at 11:05, it would reach the destination at 1:05 am.