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### Discussion :: Problems on Trains

1.  What is the speed of the train whose length is 210 metres? I. The train crosses another train (Howrah Express/12869) of 300 metres length running in opposite direction in 10 seconds. II. The train crosses another train (Howrah Express/12869) running in the same direction at the speed of 60 km/hr in 30 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 to cross the train, running in opposite directions =$${ (l1 + l2) \over (u + v)}sec$$ .

 $$10= {(210 + 300) \over (u + v)}$$

u + v = 51.

 Time taken to cross the train, running in same direction $$= {(l1 + l2) \over (u - v)} sec$$sec.

 30 = $${(210 + 300) \over (u - 60 \times )(5/18)}$$

 u = $$(17+\frac{50}{3})m/sec$$

Thus, u and v can be obtained.