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Manager
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A train crosses a bridge of length 500m in 40 seconds and a [#permalink]
 05 Mar 2005, 22:35
A train crosses a bridge of length 500m in 40 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?
187.5
375
300
250
425
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Manager
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Cloaked - Where is this question from? it doesn't sound correct, if it is would you explain ?
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SVP
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is your question complete?
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Director
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the q seems correct!
say l is the length of the train...as the speed of the train is constant
(L+500)/40 = L/15
so, L = 300 m
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Senior Manager
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300......
let length be x metres
To cross the lamp post it takes 15 sec so speed of the train = x/15
to cross the bridge it takes 40 seconds- here the key is to add the length of the bridge and the length of the train - so speed is (x+300)/40
==>x/15=(x+300)/40
solving for x, length = 300
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Manager
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cloaked_vessel wrote: the OA is 300
Cloaked , where is this question from ?
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Manager
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Thiw was an example given to me by a math tutor.
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SVP
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300
Assuming speed of the train is constant
if X is the length, then from 1st statement
speed = X/15
from 2nd speed is = (500+X)/40
X/15 = (500+X)/40
X = 300
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SVP
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Good job guys! It takes 15 seconds from the head of the train to pass a spot to the tail to pass the same spot, while it takes 40-15=25 seconds for the head to travel 500 meters. So divide 500 by five and multiply it by three you get 300.
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Manager
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(x+500)/y = 40
x/y = 15
where
x = length of the train
y = speed / second
you get
y = 20
x = 300
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close
