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### Discussion :: Problems on Trains

1. What is the length of a running train?
I.The train crosses a man in 9 seconds.

II.The train crosses a 240 metre long platform in 24 seconds

2. A.
 I alone sufficient while II alone not sufficient to answer
B.

II alone sufficient while I alone not sufficient to answer

C.
 Either I or II alone sufficient to answer
D.
 Both I and II are not sufficient to answer
E.
 Both I and II are necessary to answer

Explanation :

 Time taken by train to cross a man = $$\frac { Length of train } { Speed of train}$$       Speed = $$\frac { l } { 9 }$$....(i)

 Time taken by train to cross a platform = $$\frac {( Length of train + Length of platform) } { Speed of train}$$      Speed = $$\frac { l + 240 } { 24 }$$....(ii)

 From (i) and (ii), we get $$\frac { l } { 9 }$$= $$\frac { l+240 } { 24 }$$

Thus, l can be obtained. So both I and II are necessary to get the answer.