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  1.  What is the length of a running train crossing another 180 metre long train running in the opposite direction?

        I.The relative speed of the two trains was 150 kmph.

       II.The trains took 9 seconds to cross each other.
     

  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 :

    Let the two trains of length a metres and b metres be moving in opposite directions at u m/s and v m/s.

     

    Time taken to cross each other =   \((\frac { a+b} { u+v} ) sec\)sec.
     

     

    Now, b = 180, u + v =            \( (150\times\frac{5}{18})m/sec\)=   \( (\frac { 125 } { 3 } ) m/sec\)m/sec.
       

     

     9 =  \((\frac { a+180 } { (125/3) } )\)  
     

     a = (375 - 180) = 195 m.


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