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 4 of 24.
Prasanna Kumar said:
6 years ago
If we think let x and y be the length of the trains then, x/27,by/17 will be the speed of the trains respectively and the equation becomes x+y/23b=bx/27+y/17.
Solving we get x/y=81/34.
x+y = total distance.
23 = total time.
Speed = x/27+y/27.
Speed = distance/time.
Therefore x+y/23 = x/27+y/17 is the equation,
Can you tell me why this equation is wrong?
Solving we get x/y=81/34.
x+y = total distance.
23 = total time.
Speed = x/27+y/27.
Speed = distance/time.
Therefore x+y/23 = x/27+y/17 is the equation,
Can you tell me why this equation is wrong?
Abraham said:
6 years ago
The explanation are excellent, but we asked the the speed, so why we calculated the time taken?
Kamanulla said:
6 years ago
A = 27 - 23sec = 4sec.
B = 23 - 17sec = 6sec.
A:B = 4:6 = 2:3 in Sec.
A:B = 3:2 in Speed.
B = 23 - 17sec = 6sec.
A:B = 4:6 = 2:3 in Sec.
A:B = 3:2 in Speed.
(1)
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.
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.
Ruthvik said:
6 years ago
Why we have to take x+y in denominator? Please explain.
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?
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.
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.
ASHIS DAS said:
7 years ago
Agree @Ganapathi.
Please, anyone, give clearance.
Please, anyone, give clearance.
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