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Aristocrat
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A train traveling at 72 kmph crosses a platform Updated on: 20 Oct 2012, 02:40
Originally posted by Aristocrat on 20 Oct 2012, 00:25.
Last edited by Aristocrat on 20 Oct 2012, 02:40, edited 3 times in total.
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75% (02:12) correct 25% (01:16) wrong based on 49 sessions

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A train traveling at 72 kmph crosses a platform in 30 seconds and a man standing on the platform in 18 seconds. What is the length of the platform in meters?

A.240 meters
B.360 meters
C.420 meters
D.600 meters
E.Cannot be determined

A runs 25% faster than B and is able to give him a start of 7 meters to end a race in dead heat. What is the length of the race?

A)10 meters
B)25 meters
C)45 meters
D)15 meters
E)35 meters

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A
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E

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A train traveling at 72 kmph crosses a platform 20 Oct 2012, 01:02
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Really tricky question :)

Speed of train = 72 * (5/18) = 20 m/s

Lets consider the man as a stationery point on the platform.
Crossing the point gives us the length of the train.

Lt = 20 * 18 = 360 m.

Crossing the platform gives us the length of train & length of platform.

L(t+p) = 20 * 30 = 600 m.

So, length of platform = 600 - 360 = 240 m

IMO, Answer
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A train traveling at 72 kmph crosses a platform 20 Oct 2012, 02:33
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A runs 25% faster than B and is able to give him a start of 7 meters to end a race in dead heat.

Let the speed of b be 4x then speed of a is 1.25*4x=5x

Given by the time B runs Dkms A can cover D+7 kms

so D/4x=(D+7)/5x
5xD=4xD+ 28x
or xD= 28x
or D=28

so the length of the race is 28+7=35

Ans:E
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A train traveling at 72 kmph crosses a platform 20 Oct 2012, 02:35
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Aristocrat
A train traveling at 72 kmph crosses a platform in 30 seconds and a man standing on the platform in 18 seconds. What is the length of the platform in meters?

A.240 meters
B.360 meters
C.420 meters
D.600 meters
E.Cannot be determined

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Speed is in kmph but other info is in secs so convert speed to m/s

72 kmph = (5/18)*72 = 20 m/s

Why does the train take longer to cross the platform as compared to the time taken to cross the man? Because the platform is long and the train has to cover the platform's length too. To cover the platform's length, the train takes 30 - 18 = 12 secs more.
In 12 secs, the train covers 12*20 = 240 m.

So the length of the platform must be 240 m
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A train traveling at 72 kmph crosses a platform 20 Oct 2012, 02:39
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Aristocrat


A runs 25% faster than B and is able to give him a start of 7 meters to end a race in dead heat. What is the length of the race?

10 meters
25 meters
45 meters
15 meters
35 meters
Show more

Use ratios:

A's speed : B's speed = 5:4
In the same time, distance covered by A:distance covered by B = 5:4
This difference of 1 is equal to 7 m i.e. the difference between the distance covered by A and distance covered by B.
So the length of the race track must be 5*7 = 35 m (because A covers the entire track so the length of the track is given by 5*7)

For more on ratios, check:
https://www.gmatclub.com/forum/veritas-prep-resource-links-no-longer-available-399979.html#/2011/0 ... of-ratios/

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