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.
Nayan said:
4 years ago
(x - 1.25) x 8.4 = (x - 1.5) x 8.5.
At this stage, if I multiply both sides with 10. And try to do the solution. The result will change. Result = 117 m/sec.
At this stage, if I multiply both sides with 10. And try to do the solution. The result will change. Result = 117 m/sec.
(1)
Arsh said:
9 years ago
Can anybody tell me the shortcut method because in entrance exam there is not much time to make and solve equations?
Sumithra said:
7 years ago
For m/sec to km/hr conversion, we need to multiply with 18/5 only know.
Then why here it is multiplied with 5/18.
Then why here it is multiplied with 5/18.
(2)
Anomee said:
6 years ago
Average speed means it compared the speed of one vehicle. Relative speed means it compared the spd of 2 vehicles.
Vinay said:
1 decade ago
But as manasa said why to equal both the relative speed's.
I am not understanding. Can any one please help me.
I am not understanding. Can any one please help me.
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.
Sweta said:
7 years ago
Hi, Can anyone tell me, what is the basic difference between Relative and Average speed?
(2)
Sanket said:
1 decade ago
In this step:
(x - 1.25) x 8.4 = (x - 1.5) x 8.5.
Why " x-1.25 " taken?
(x - 1.25) x 8.4 = (x - 1.5) x 8.5.
Why " x-1.25 " taken?
Kavi said:
9 years ago
In the answer, x is distance because speed * time, how come you say that x is speed?
PrasannKumar said:
8 years ago
@Priyanka.
Both are the distances of the train only to get the answer he equated.
Both are the distances of the train only to get the answer he equated.
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