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 4 of 6.
BALIRAM said:
1 decade ago
When add the speed and when subtract the speed in the case two train.
Nitishkumar said:
1 decade ago
The two train and man are moving in same direction.
So the relative speed = x-5.4 & another we write that other man, x-4.5 train length is constant that's by distance will be equal.
So the relative speed = x-5.4 & another we write that other man, x-4.5 train length is constant that's by distance will be equal.
Harshad said:
1 decade ago
@Siva.
The length of the train is the distance.
In our case its (x - 1.25) x 8.4 OR (x - 1.5) x 8.5.
When we equate we got x = 22.5.
So substitute in any equation.
And we get length as 178.5 m.
The length of the train is the distance.
In our case its (x - 1.25) x 8.4 OR (x - 1.5) x 8.5.
When we equate we got x = 22.5.
So substitute in any equation.
And we get length as 178.5 m.
Siva said:
1 decade ago
If the question is to find the length of the train, then how to solve it?
Haphyz said:
1 decade ago
Since we are calculating relative speeds, the value of the distance can only imply the length of the train which is constant. Hence the need to equate both distances.
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?
Vaisakh said:
1 decade ago
Just covert seconds to hour by dividing 60x60 = 3600.
No more conversions:
Let length be x.
and Speed be y.
8.4/3600 = x/(y-4.5).
8.4y -37.80 = 3600x ...(eq 1).
8.5/3600 = x/(y-5.4).
8.5y-45.90 = 3600x....(eq 2).
Solving both equations will give you, y= 81kmph.
No more conversions:
Let length be x.
and Speed be y.
8.4/3600 = x/(y-4.5).
8.4y -37.80 = 3600x ...(eq 1).
8.5/3600 = x/(y-5.4).
8.5y-45.90 = 3600x....(eq 2).
Solving both equations will give you, y= 81kmph.
Suan said:
1 decade ago
We don't necessarily have to use the conversion of kmph to m/s here since the unnecessary units (sec) eventually cancel out each other on the subsequent steps of solution.
Tinku majumder said:
1 decade ago
How 5/18 Came?
Divya said:
1 decade ago
Thank you manasa. Nice explanation.
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