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# Two trains, 400 and 320 metres long take a minute to cross

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Senior Manager
Joined: 30 Aug 2003
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Two trains, 400 and 320 metres long take a minute to cross [#permalink]  16 Jan 2004, 12:24
Two trains, 400 and 320 metres long take a minute to cross each other while travelling in the same direction and take only 10 seconds when they cross in opposite directions. What is the speed of the faster train?
{1km/hr=5/18m/s}

a.32kmph
b.126
c.108
d.42
e.None of these
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[#permalink]  16 Jan 2004, 14:29
E, none of these? I am getting 151.2 kmph. Let the speeds of the train be x & y mps, so when they are travelling in the same direction we subtract speeds and in the opposite direction we add speeds becoz of the Relative speed.
Length of both the trains = 720 ,
so 720/(x-y) = 60 secs and so x-y = 12 mps ------------ (1)

720/(x+y) = 10 secs and so x+y = 72 mps ------------(2)

solving for x and y we get x=42 mps and y= 30 mps and 42 mps= 151.2 kmph
Senior Manager
Joined: 30 Aug 2003
Posts: 330
Location: BACARDIVILLE
Followers: 1

Kudos [?]: 1 [0], given: 0

[#permalink]  16 Jan 2004, 14:32

_________________

Pls include reasoning along with all answer posts.
****GMAT Loco****
Este examen me conduce jodiendo loco

[#permalink] 16 Jan 2004, 14:32
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# Two trains, 400 and 320 metres long take a minute to cross

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