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 2 of 5.
Ranjith said:
6 years ago
Well I have a little doubt in here, why can't we take the length of another train as 2x and length of this train as X so the things won't change but I can't get the ans, someone make me clear about this.
Prabu said:
1 decade ago
After found the length of the first train then it will come to know about the length of 2nd train because (x/2).
When we find the length of the platform. Why did we use the first train length?
When we find the length of the platform. Why did we use the first train length?
Lalit said:
1 decade ago
Why we are not calculating directly platform length as we have speed of train ie. 48 km and.
Sec to cross platform ie. 45 sec.
So 48*5/18 = x/45 (x is distance).
X = 600.
Sec to cross platform ie. 45 sec.
So 48*5/18 = x/45 (x is distance).
X = 600.
G.One said:
6 years ago
@Ranjith.
In Qn. clearly mentioned as another train length is half of the first train's length than the length of another train would be (x/2) or 0.5x rather than 2x.
In Qn. clearly mentioned as another train length is half of the first train's length than the length of another train would be (x/2) or 0.5x rather than 2x.
Chitti said:
1 decade ago
Why we taken first train speed is because the first train passes the second train and also passes the platform so we taken first train speed 48kmph.
Ramyajit said:
1 decade ago
@PRIYA
u r wrong.The length of the train is 200m.
To finding length of the platform,u have to solve this manner.
200+x=48*(5/18)*45
ANS:- 400m.
u r wrong.The length of the train is 200m.
To finding length of the platform,u have to solve this manner.
200+x=48*(5/18)*45
ANS:- 400m.
Rani said:
1 decade ago
Why they have substituted time as 12 why not 25?
The problem is related to length of platform not the length of train.
Can any one explain this?
The problem is related to length of platform not the length of train.
Can any one explain this?
Ayesha said:
1 decade ago
@Prabha.
i.e., Because you are considering the length of first train ie. 200m. So you have to take the speed of first train only.
i.e., Because you are considering the length of first train ie. 200m. So you have to take the speed of first train only.
Prabir kumar kar said:
1 decade ago
12 sec is used to cross both the train from opposite direction.but 45 sec is used to pass only the platform by the fastest train.
Chandan.b said:
7 years ago
Can anybody explain this step for me?
x + (x/2)] = 12 or
3x = 300
or x = 200.
Therefore Length of first train = 200 m.
x + (x/2)] = 12 or
3x = 300
or x = 200.
Therefore Length of first train = 200 m.
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