Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 29)
29.
A train travelling at 48 kmph completely crosses another train having half its length and travelling in opposite direction at 42 kmph, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the platform is
Answer: Option
Explanation:
Let the length of the first train be x metres.
| Then, the length of the second train is |  |
x |  |
metres. |
| 2 |
| Relative speed = (48 + 42) kmph = | |
90 x | 5 | |
m/sec = 25 m/sec. |
| 18 |
 |
[x + (x/2)] | = 12 or | 3x | = 300 or x = 200. |
| 25 | 2 |
Length of first train = 200 m.
Let the length of platform be y metres.
| Speed of the first train = | |
48 x | 5 | |
m/sec = | 40 | m/sec. |
| 18 | 3 |
| (200 + y) x |
3 | = 45 |
| 40 |
600 + 3y = 1800
y = 400 m.
Discussion:
48 comments Page 3 of 5.
Arman said:
1 decade ago
If we take 2x and x as speeds of the trains, then its changing from what it is when we take x and x/2 as two train speeds.
Piyush said:
1 decade ago
Correct Answer is 200m.
Two cross Platform Distance would be 400+y.
i.e. If train length is 200 than it should be 400+y.
Two cross Platform Distance would be 400+y.
i.e. If train length is 200 than it should be 400+y.
Prabha said:
1 decade ago
Please tell me why we have to use 48km ? why not 42 km ?
after finding x=200...?? do answer it.
ie..200+x=48*(5/18)*45
after finding x=200...?? do answer it.
ie..200+x=48*(5/18)*45
Reka said:
8 years ago
Can anybody tell me why they have taken the 1st train to calculate the length of the platform, why not both the trains.
Nakul gowda said:
1 decade ago
@Vineet:
You are wrong buddy,,..you have to add train's length as well.
So it'd be 400+200=600/45*18/5 = 48 kmph.
You are wrong buddy,,..you have to add train's length as well.
So it'd be 400+200=600/45*18/5 = 48 kmph.
Umang said:
8 years ago
@Reka.
Here in this question condition is given that only first train cross the railway platform in 45 seconds.
Here in this question condition is given that only first train cross the railway platform in 45 seconds.
Raj said:
4 years ago
Guys,
Why can't we assume length of 1st train 2L metres and length of 2nd train L metres?
Please explain me.
Why can't we assume length of 1st train 2L metres and length of 2nd train L metres?
Please explain me.
(3)
Riya said:
7 years ago
Can anybody help me?
Why we are taking the first train speed for calculating the length of the platform?
Why we are taking the first train speed for calculating the length of the platform?
Priya said:
1 decade ago
I think answer for length of the platform is 200m.
(400+y) /45=48*5/18.
Solving this we get y=200m.
(400+y) /45=48*5/18.
Solving this we get y=200m.
Suraj said:
9 years ago
@Lakhbir.
5/18 is used when converting kmph to mps.
18/5 is used when converting mps to kmph.
5/18 is used when converting kmph to mps.
18/5 is used when converting mps to kmph.
(1)
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers