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### Discussion :: Problems on Trains

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

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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