Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 28)
28.
A train overtakes two persons walking along a railway track. The first one walks at 4.5 km/hr. The other one walks at 5.4 km/hr. The train needs 8.4 and 8.5 seconds respectively to overtake them. What is the speed of the train if both the persons are walking in the same direction as the train?
Answer: Option
Explanation:
| 4.5 km/hr = |  |
4.5 x | 5 |  |
m/sec = | 5 | m/sec = 1.25 m/sec, and |
| 18 | 4 |
| 5.4 km/hr = | |
5.4 x | 5 | |
m/sec = | 3 | m/sec = 1.5 m/sec. |
| 18 | 2 |
Let the speed of the train be x m/sec.
Then, (x - 1.25) x 8.4 = (x - 1.5) x 8.5
8.4x - 10.5 = 8.5x - 12.75
0.1x = 2.25
x = 22.5
 Speed of the train = |
|
22.5 x | 18 | |
km/hr = 81 km/hr. |
| 5 |
Discussion:
54 comments Page 3 of 6.
Swapnil said:
8 years ago
Both equations is equated because, distance cover by train for both the person is same, ie. Length of the train.
So in solution calculate the distance cover by train (length of the train) for both the person from given data and then equated them. Because distance covered by train (length of the train) is same for both the person.
So in solution calculate the distance cover by train (length of the train) for both the person from given data and then equated them. Because distance covered by train (length of the train) is same for both the person.
Sanjeev said:
8 years ago
Can't understand. Please explain me in detail.
Rahul said:
8 years ago
Thanks for explaining the solution @Swapnil.
Anomee said:
7 years ago
Average speed means it compared the speed of one vehicle. Relative speed means it compared the spd of 2 vehicles.
Prasanna said:
6 years ago
Answer is 81km/hr.
Aditya said:
6 years ago
Solve it by taking a reference frame for observation from Man1 4.5 kph. It would make calculation much easier.
Rrrr said:
5 years ago
The answer should be 80.
Divya said:
1 decade ago
Thank you manasa. Nice explanation.
Nitesh Nandwana said:
2 decades ago
Hi Chanda,
If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:
(A's speed) : (B's speed) = (b : a)
If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:
(A's speed) : (B's speed) = (b : a)
Deepika said:
2 decades ago
Please explain me only the last step.
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