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by georgeanand » Wed Nov 03, 2010 6:29 am
Two trains A and B each of length 100m travel in opposite direction in tracks. The speeds are 20m/s and 30m/s respectively. A boy sitting in the front end of train A, throws a ball to a boy sitting in the front end of train B, when they are at the closest distance. The speed of the ball is 2m/s. The ball instead of reaching the boy hits the rear end of the train. Find the distance between the parallel tracks.
A.3 m B.4m C.6m D.5m E.7m

Try this problem by
1. Diagraming the problem and understanding the path traced by the 3 objects
2. Deriving a relationship between the moving elements
3. Framing an equation
4. Solving the equation

Let me know your answer... :D

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by gmatjeet » Fri Nov 05, 2010 7:37 am
Answer is E = 7 m

time taken is equal

T = T

D/2 = 100/30

D = 20/3
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by georgeanand » Sat Nov 06, 2010 3:16 am
i dont think that is the answer. time is the same is correct. use relative velocity
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by limestone » Sat Nov 06, 2010 9:20 am
The two trains will cross each other at a speed of: 20 + 30 = 50m/s ( as they are moving in opposite direction).

When the two trains meet (or when the two boys at the closest distance), one boy through a ball to another boy. The ball hit the end rear of the train.

It means the time for the ball to pass the distance between the two trains equal to the time for the two train to travel a full length of 100m.

So the time the ball traveled is : 100/50 = 2s.
Distance the ball traveled: 2 * 2 = 4m
IMO: B is the answer.
Anyway, is this a GMAT question?
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by georgeanand » Sun Nov 07, 2010 8:08 am
limestone wrote:The two trains will cross each other at a speed of: 20 + 30 = 50m/s ( as they are moving in opposite direction).

When the two trains meet (or when the two boys at the closest distance), one boy through a ball to another boy. The ball hit the end rear of the train.

It means the time for the ball to pass the distance between the two trains equal to the time for the two train to travel a full length of 100m.

So the time the ball traveled is : 100/50 = 2s.
Distance the ball traveled: 2 * 2 = 4m
IMO: B is the answer.
Anyway, is this a GMAT question?
correct. this type of reasoning i presume is tested for 750+ problems... i will upload more sums like this...
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by Jim@Grockit » Sun Nov 14, 2010 7:29 pm
georgeanand wrote:
limestone wrote:The two trains will cross each other at a speed of: 20 + 30 = 50m/s ( as they are moving in opposite direction).

When the two trains meet (or when the two boys at the closest distance), one boy through a ball to another boy. The ball hit the end rear of the train.

It means the time for the ball to pass the distance between the two trains equal to the time for the two train to travel a full length of 100m.

So the time the ball traveled is : 100/50 = 2s.
Distance the ball traveled: 2 * 2 = 4m
IMO: B is the answer.
Anyway, is this a GMAT question?
correct. this type of reasoning i presume is tested for 750+ problems... i will upload more sums like this...
I think this is a bit beyond the reasoning required on the GMAT; perhaps there should be a part of the forum for people who want to be challenged in this way as part of their preparation?
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by georgeanand » Mon Nov 15, 2010 7:06 pm
Jim@Grockit wrote:
georgeanand wrote:
limestone wrote:The two trains will cross each other at a speed of: 20 + 30 = 50m/s ( as they are moving in opposite direction).

When the two trains meet (or when the two boys at the closest distance), one boy through a ball to another boy. The ball hit the end rear of the train.

It means the time for the ball to pass the distance between the two trains equal to the time for the two train to travel a full length of 100m.

So the time the ball traveled is : 100/50 = 2s.
Distance the ball traveled: 2 * 2 = 4m
IMO: B is the answer.
Anyway, is this a GMAT question?
correct. this type of reasoning i presume is tested for 750+ problems... i will upload more sums like this...
I think this is a bit beyond the reasoning required on the GMAT; perhaps there should be a part of the forum for people who want to be challenged in this way as part of their preparation?
I presume if people want to aim for 750+ , they should be ready to handle sums like this... I guess this type of creative problem solving will help them crack tougher questions in the GMAT.

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