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.
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. |
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.
Time = Distance/Speed.
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.
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.
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.