Problems on Trains - General Aptitude

Q1:

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 answe

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

ANS:E - Both I and II are necessary to answer

Time taken to cross the train, running in opposite directions	=	(l₁ + l₂)	sec.
		(u + v)

10 =	(210 + 300)
	(u + v)

u + v = 51.

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

30 =	(210 + 300)
	(u - 60 x (5/18))

u =		17 +	50	m/sec.
			3

Thus, u and v can be obtained.

Correct answer is (E).