Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 4)
4.
Two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 23 seconds. The ratio of their speeds is:
Answer: Option
Explanation:
Let the speeds of the two trains be x m/sec and y m/sec respectively.
Then, length of the first train = 27x metres,
and length of the second train = 17y metres.
 |
27x + 17y | = 23 |
| x+ y |
27x + 17y = 23x + 23y
4x = 6y
| |
x | = | 3 | . |
| y | 2 |
Discussion:
233 comments Page 20 of 24.
Vidhyadhar said:
7 years ago
Let x=speed of train 1.
And y=speed of train 2.
Our task=x/y.
So, length of 1st train (d1)=x*27(dist=speed*time)
So, 2nd (d2) = y * 17.
Time taken by trains to cross each other =23 sec.
Time =dist/speed.
23=(d1+d2)/x+y.
23=(27*x+17*y)/x+y.
By solving this we get.
Result = x/y = 3/2
And y=speed of train 2.
Our task=x/y.
So, length of 1st train (d1)=x*27(dist=speed*time)
So, 2nd (d2) = y * 17.
Time taken by trains to cross each other =23 sec.
Time =dist/speed.
23=(d1+d2)/x+y.
23=(27*x+17*y)/x+y.
By solving this we get.
Result = x/y = 3/2
Kavya said:
7 years ago
Good answer, Thanks @Shyam.
Ganapathi said:
7 years ago
Time taken by 1st train is more than the 2nd train then how speed ratio of 1st train is more than second train? I am not getting this. Please tell me.
ASHIS DAS said:
7 years ago
Agree @Ganapathi.
Please, anyone, give clearance.
Please, anyone, give clearance.
Nagendra said:
7 years ago
@Ganapathi, @Ashish Das,
The length of 1st Train is too long compared to 2nd Train. Hence even if though if it is faster, it took more time to cross the man.
The length of 1st Train is too long compared to 2nd Train. Hence even if though if it is faster, it took more time to cross the man.
Kumar said:
7 years ago
Distance = speed * time.
Time = 23 sec.
Time = total distance/speed,
Total distance = 27x+17y
The relative speed = x+y (opposite direction).
(27x+17y/x+y) = 23.
Time = 23 sec.
Time = total distance/speed,
Total distance = 27x+17y
The relative speed = x+y (opposite direction).
(27x+17y/x+y) = 23.
Divya. A said:
7 years ago
Here distance is not mentioned. But you took 27 and 17 as distance. How can we take time interms of distance? Can anyone please explain?
Ruthvik said:
6 years ago
Why we have to take x+y in denominator? Please explain.
Aditya said:
6 years ago
Distance is not relative why we add both the lengths?
We should only take either of them.
We should only take either of them.
Shivam Mehta said:
6 years ago
Let the speed of 1st train be X and 2nd be Y.
So, the distance of 1st train (D= S*T) 27X and 2nd 17Y.
Speed of 2 objects get added if they are in opp direction.
So, speed = X+Y , T= D/S
Then 23= (27X + 17Y)/ X+Y.
So, the distance of 1st train (D= S*T) 27X and 2nd 17Y.
Speed of 2 objects get added if they are in opp direction.
So, speed = X+Y , T= D/S
Then 23= (27X + 17Y)/ X+Y.
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