Data Sufficiency 3
Practice and master this topic with our carefully crafted questions.
(Question 1 to 3) : 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.
What is the length of a running train P crossing another running train Q?
I. These two trains take 18 seconds to cross each other.
II. These trains are running in opposite directions.
III. The length of the train Q is 180 metres.
Let the length of the train P be x metres.
II. These trains are running in opposite directions.
III. Length of the train Q is 180 m.
I. Time taken by P to cross Q
| (180 + x) |  18 = |
(180 + x) | |
| Relative speed | Relative speed |
Thus, even with I, II and III, the answer cannot be obtained.
Correct answer is (E).
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 and 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 |
| 10 | 5 |
= 72 km/hr.
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.
How much time will the train A take to cross another train B running in opposite direction?
I. Train A crosses a signal pole in 6 seconds.
II. Ratio of the speeds of train A and B is 3 : 2.
III. Length of the two trains together is 500 metres.
II. Let the speeds of A and B be 3x m/sec and 2x m/sec.
I. Length of train A = 3x X 6 m = 18x metres.
III. Length of train B = 500 - 18x m.
Relative speed = 3x + 2x m/sec
= 5x m/sec.
Time taken by A to cross B = Sum of their lengths/ Relative speed
= 500/5x sec.
Thus, even with the information in all the three statements, question cannot be answered.
Correct answer is (E).