Discussion :: Problems on Trains

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.
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.


E.
Both I and II are necessary to answer 
Answer : Option E
Explanation :
Time taken to cross the train, running in opposite directions 
=  \(\frac { (l1+l2) } { (u+v) } sec\)  
10 = \(\frac { (210+300) } { (u+v) } \)  
u + v = 51.
Time taken to cross the train, running in same direction =  \( \frac { (l1+l2) } { (uv) } sec\)sec.  
30 = \(\frac { (210+300) } { ((u60) \times(5/8))} sec\)  
u = \( (17+\frac{50}{3})m/sec\)  Thus, u and v can be obtained. 
Correct answer is (E).
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