Aptitude - Problems on Trains

Each of the questions given below consists of a statement and / or a question and two statements numbered I and II given below it. You have to decide whether the data provided in the statement(s) is / are sufficient to answer the given question. Read the both statements and

  • Give answer (A) if the data in Statement I alone are sufficient to answer the question, while the data in Statement II alone are not sufficient to answer the question.
  • Give answer (B) if the data in Statement II alone are sufficient to answer the question, while the data in Statement I alone are not sufficient to answer the question.
  • Give answer (C) if the data either in Statement I or in Statement II alone are sufficient to answer the question.
  • Give answer (D) if the data even in both Statements I and II together are not sufficient to answer the question.
  • Give answer(E) if the data in both Statements I and II together are necessary to answer the question.
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.

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

Answer: Option E

Explanation:

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).


2. 

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.

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

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 = (a + b) sec.
(u + v)

Now, b = 180, u + v = 150 x 5 m/sec = 125 m/sec.
18 3

9 = a + 180
(125/3)

a = (375 - 180) = 195 m.


3. 

What is the length of a running train?

I. 

The train crosses a man in 9 seconds.

 II. 

The train crosses a 240 metre long platform in 24 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. Both I and II are not sufficient to answer
E. Both I and II are necessary to answer

Answer: Option E

Explanation:

Time taken by train to cross a man = Length of train       Speed = l ....(i)
Speed of train 9

Time taken by train
to cross a platform =
(Length of train +
Length of platform)
     Speed = l + 240 ....(ii)
Speed of train 24

From (i) and (ii), we get l = l + 240 .
9 24

Thus, l can be obtained. So both I and II are necessary to get the answer.

The correct answer is (E).