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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

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    Answer : Option E

    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.

     The correct answer is (E).


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