Aptitude - Problems on Trains - Discussion

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).


Sundar said: (Apr 9, 2011)  
Since in both statement reveals that the another train is "Howrah Express/12869" and its length is 300 meters.

Therefore, we can find the answer with I and II.

If it is not specified (if not included the another trains details specifically), it may be different trains and different length. In this case, the answer will be "Both I and II are not sufficient to answer".

Hope this will help you a little bit.

Senthil said: (Jan 3, 2012)  
Thanks Sundar

Aditya Nath said: (Sep 3, 2012)  
The question asks only for the speed of train which is 210m long and nothing of the Howrah Exp./12869... So statement II is sufficient alone.

Akanksha said: (Sep 9, 2012)  
@Aditya is rite.

Gautam Kumar said: (Sep 21, 2012)  
I don't think that option E is right. According to me option D is correct. This is because in the option I & II given in question it is specially mentioned Train number & Train name i.e. Howrah Express 12869. Now what I want to say that the same train can't run in both same & opposite direction at one time.

Rakshit said: (Jan 27, 2013)  
We can find speed by Ist statement by using formula s=d/t
d=300+210=510
t=10 sec
s=51m/sec.

Using relative speed formula we can
S1+S2=D1/T
S1=x
S2=51m/sec
D1=210
T=10 sec.

A.Srikanth said: (Jul 5, 2013)  
What @Sunder said it is right.

And what @GAUTHM KUMAR said is just like he showing his sense of humor. The answer E is correct.

And coming to @Adithya.

With out knowing the length of second train how you are going to find speed of first train ?

Gagan Mathur said: (Sep 17, 2013)  
One of the trains speed is given. All we have to do is use the formula time to cross each other = (l1+l2)/(u-v).

Adsam said: (Jul 11, 2014)  
II alone sufficient since only the speed of 210m train is asked.

Kausar Shamim said: (Aug 4, 2014)  
According to me option E is not right as statement II alone is needed to find the speed of the train.

Vivek Kumar said: (Aug 30, 2014)  
Statement 2 is sufficient to find out the velocity of train having length 210m. So given answer is wrong.

Raja said: (Sep 22, 2014)  
@Kausar and @Vivek without knowing the length of the other train how would you find velocity of other train ?

Parthshah said: (Dec 26, 2014)  
It is very simple. To find out two unknown variable we need two equations. So @Sundar is right.

Janvi said: (Feb 4, 2015)  
Sorry but I am confuse about this question please can any explain me in detail.

Sourav Saha said: (Jul 7, 2015)  
In the problem using statement I we can find out the sum of the speeds of both the train u+v=51 -- (1) and can't we use the speed of the second train i.e. 60 km/hr and replace it in equation 1?

The results are 103/3 by replacing. And 101/3 by following the method given in the site.

Why is this difference in the result?

Lokesh said: (Jul 20, 2015)  
Please anyone explain me. I think the answer is 'D' but it was 'E'. Why?

Utsav Bansal said: (Jul 31, 2015)  
Option E is okay, just see the instruction guys both statements together are necessary to answer this question as from stat-1 you will get the length of other train n using stat-2 data you can calculate the speed easily, one thing that I find ambiguous is that both statements are contradicting as in 1st one train is moving in opposite direction while in 2nd one same train is moving in same direction.

Udita Mandal said: (Dec 16, 2015)  
Hi, I think correct answer is 'B' because according to the question we have to find out only speed of train with length 210 m i.e. 'u', which can be satisfactorily found out by the information given in option 2, there is no need of finding value of 'v', and none of information given in option 1 is helpful in finding out the answer.

So correct answer according to me is 'B' only option 2 is sufficient to answer the given question. Please go through my suggestion and if I am wrong then correct my doubt.

Thank you!

M.Homesh said: (Aug 2, 2016)  
We can also solve it by using the relative speed method.

S1 + S2 = D1/T.

Shubham said: (Sep 24, 2016)  
Statement 2 is sufficient.

Vidhya said: (Feb 2, 2017)  
Yes, you are right @Gautam Kumar.

Hari said: (Feb 22, 2017)  
Only statement ii is sufficient to find the speed of the train asked in question but the statement I gives the length of the train. So we are using the length of train specified in statement I and substituting in statement II. So if statement I is not given we don't know the length of the train which we will substitute in statement II as per below.

Based on statement II.

Time taken to cross the train, running in same direction = (l1 + l2) / (u - v) (l1=given in question; l2= given in statement II; v= given in statement II; u = speed of train).

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

u = (17 +50/3) which is the speed of train asked in the question.

Therefore E is the correct answer.

Anuj said: (Feb 28, 2017)  
Actually, I have a doubt on this question a tree and having a length of 350 metre cross the bridge length 750 m. If the speed of the train is 55 kilometre per hour how much time will the train take to cross the bridge?

Can anyone solve this?

Kriti said: (Jul 20, 2017)  
Option (B) is the correct answer since statement II alone is sufficient to find the answer.

Priyanka said: (Mar 12, 2018)  
I think statement 2 is sufficient.

Dhanupatil said: (Apr 9, 2018)  
V in sec, how it is (5/18)?

Pankaj said: (Apr 11, 2018)  
Agree @A. Srikanth &@ditya. I miss length of the 2nd train. Thanks.

Sakshi Amrutkar said: (Jun 2, 2018)  
In the above given question where the length of a train is mentioned? please explain about it.

Rathod said: (Jun 18, 2018)  
u=606/5 not (17+50/3=101/3 it is not right).

Utkarsh Saxena said: (Feb 22, 2019)  
Option E is correct because the length of the second train that is 300 m is given in statement 1 without it you cannot find the answer.

Shanthkumar said: (Jul 5, 2019)  
Considering the direction of trains as per statement 1 i.e. opposite direction and statement 2 i.e the same direction so we need both statements to find train speed in both directions respectively.

Vinayak N Kamath said: (Jul 25, 2019)  
As they have asked about the speed of train that is 210m long. So data 2 is sufficient to answer.

Mandal said: (Aug 27, 2019)  
How is statement 2 sufficient? can anyone explain it in details that only statement 2 is sufficient?

Akash C P said: (Nov 13, 2019)  
We are not using the relation u+v=51 to find the final answer so statement 2 alone is sufficient, option B is right.

Amit Kumar said: (Dec 18, 2019)  
Anuj it will take 0.02 hours to cross the Bridge.

Nishanth Mekala said: (Mar 22, 2020)  
The speed of the train can be retrieved from statement 2 alone.

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