Aptitude - Problems on Trains - Discussion

Discussion Forum : Problems on Trains - Data Sufficiency 3 (Q.No. 1)
Directions to Solve

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.

I only
II only
III only
II and III only
All I, II and III are required.
Answer: Option
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.

Discussion:
31 comments Page 2 of 4.

Amar said:   8 years ago
Can you please explain 20*18/5 how did you got 18/5?

Anshul said:   8 years ago
I is redundant but III can also be regarded as redundant because the speed can be calculated from I and II too.
(1)

Abhinav kumat said:   9 years ago
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.

Chirag said:   9 years ago
Why 558 divide by 72?

Priya said:   9 years ago
Can anyone explain me why in explanation of III multiplies 20 with 18/5?

Snehasish said:   9 years ago
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.

Prema said:   9 years ago
I didn't understand the last step. How the answer becomes 3 pm?

Prema said:   9 years ago
I didn't understand the last step. How the answer becomes 3 pm?

Argha said:   9 years ago
According to the question we have to choose the redundant one, and that is I, so the answer should be A.

Aritra Basu said:   10 years ago
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.


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