Aptitude - Problems on Trains - Discussion

Each of these questions is followed by three statements. You have to study the question and all the three statements given to decide whether any information provided in the statement(s) is redundant and can be dispensed with while answering the given question.

1. 

At what time will the train reach city X from city Y?

I. 

The train crosses another train of equal length of 200 metres and running in opposite directions in 15 seconds.

II. 

The train leaves city Y at 7.15 a.m. for city X situated at a distance of 558 km.

 III. 

The 200 metres long train crosses a signal pole in 10 seconds.

[A]. I only
[B]. II only
[C]. III only
[D]. II and III only
[E]. All I, II and III are required.

Answer: Option D

Explanation:

From the statement I, we get length of the train is 200 metres (Redundant info while comparing with Statement III). The rest of the info given in this statement cannot be used for calculating the speed of the train, because the two trains might run at different speed.

III gives, speed = 200 m/sec = 20 m/sec = 20 x 18 km/hr = 72 km/hr.
10 5

II gives, time taken = 558 hrs = 31 hrs = 7 3 hrs = 7 hrs 45 min.
72 4 4

So, the train will reach city X at 3 p.m.

Hence II and III only gives the answer.


Anu said: (Mar 19, 2011)  
Can anyone explain why 72 divides 558km.

Leeba said: (Jun 9, 2011)  
Because,

Time = Distance/Speed.

Vinod Agrawal said: (Jun 26, 2011)  
Just to get the time taken by the train to reach at City Y.

Master said: (Aug 23, 2011)  
The answer should be A.

The question clearly says which information is redundant & can be dispensed. Statement I is not required to solve it, so answer should be option A.

Richu said: (Jan 26, 2012)  
Ya me too agreeing with you @Mr Master.

First sentence is not telling about the speed of the second train.

Also second and third statements are also not telling about the speed of the second train. So First sentence is unnecesssary.

The explanation given to it is correct but the answer option is wrong.

Harish said: (Apr 11, 2012)  
Hello, Please explain me this problem briefly.

Kamal said: (Oct 27, 2013)  
In first statement we know the length of each train so it is not waste statement.

Arash said: (Mar 15, 2014)  
So I is redundant and A is correct. Why the correct answer is chosen D?

Fgyugu said: (Aug 14, 2014)  
Speed of the train can be found out by using statement 1.

As (200+200)/15 = 26.66 is relative speed of train A to train B,

Since speed of B=200/10=20, Therefore speed of A = 26.66-20 = 6.66,

Thus all the statements are required.

Shyam said: (Aug 23, 2014)  
Answer should be E, because without using statement 1 we can't take length of train 200m.

Amrish Choudhary said: (Nov 11, 2014)  
Correction required in the answer because according to question option A is correct!

Aritra Basu said: (Mar 10, 2015)  
The correct answer is E Since III is required to calculated the speed of the second train, which can be used to get the speed of original train by using I. Then II can be used to get the answer.

Argha said: (Jun 20, 2015)  
According to the question we have to choose the redundant one, and that is I, so the answer should be A.

Prema said: (Jul 12, 2015)  
I didn't understand the last step. How the answer becomes 3 pm?

Prema said: (Jul 12, 2015)  
I didn't understand the last step. How the answer becomes 3 pm?

Snehasish said: (Aug 23, 2015)  
Firstly, as many others have pointed out, we have to tell which one or ones of the given pieces of information is or are redundant and can be dispensed with while answering the question. According to this, option A is the correct answer, because we can answer the question using only information II and information III.

Secondly, if we were to tell which information are sufficient to answer the question, then the correct answer will be D.I don't understand why some people are saying the correct answer will be E in this case, do they have any doubt that the given solution is not able to find the reaching time of the train? In other words, the solution is wrong? No friends, the "solution" is correct.

Thirdly, @Prema:

Time taken to reach at station X is 7 hrs 45 mins.

Starting time = 7:15 am, so reaching time will be (7:15 am + 7 hrs 45 mins) which is nothing but 3 pm.

Priya said: (Oct 30, 2015)  
Can anyone explain me why in explanation of III multiplies 20 with 18/5?

Chirag said: (Jan 20, 2016)  
Why 558 divide by 72?

Abhinav Kumat said: (May 1, 2016)  
I can't understand this answer. According to the question we have to find out which is redundant? So, how answer becomes D?

I think the answer should which is not required to solve the Question.

Please clear my confusion.

Anshul said: (Aug 21, 2016)  
I is redundant but III can also be regarded as redundant because the speed can be calculated from I and II too.

Amar said: (Feb 21, 2017)  
Can you please explain 20*18/5 how did you got 18/5?

Shubham said: (Jun 14, 2017)  
18/5 is simply multiplied to convert m/s into km/hr.

1m/s = (1m/1000)km/(1s/60 * 60)hr,
= (1/1000)km/(1/3600)hr,
= 3600/1000,
= (18/5) km/hr.

It is the factor of converting 1m/s. So it has been multiplied directly.

Shubham said: (Jul 15, 2017)  
Question is to identify the redundant statement, so the answer should be 1 right?

Kittu said: (Jan 14, 2018)  
Redundant means unnecessary. That means which one is unnecessary. Then how option d is the answer?

Somya Gupta said: (Jul 28, 2018)  
How 3pm? I can't understand anyone explain.

Vianny said: (Oct 18, 2018)  
Can anyone explain 558/72?

Basil said: (Jun 3, 2019)  
Here, It was to identify the redundant criteria. How it was II and III only? Please explain in detail.

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