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:
238 comments Page 23 of 24.
Kartik said:
2 decades ago
Excellent explanation SRI.
Sri said:
2 decades ago
Let the speeds of the two trains be x m/sec and y m/sec respectively.
Then, length of the first train = 27x metres,(length=speed*time..so length=x*27=27x metres)
and length of the second train = 17y metres.(length=speed*time..so length=y*17=17y metres)
If two trains of length a metres and b metres are moving in opposite directions at u m/s and v m/s, then:
Relative speed of the trains =x+y(since they are moving in opp direction)
Total distance covered = L1+L2
So time taken to cross each other = total distance /relative speed
Hence 23=(27x+17y)/(x+y)
Then, length of the first train = 27x metres,(length=speed*time..so length=x*27=27x metres)
and length of the second train = 17y metres.(length=speed*time..so length=y*17=17y metres)
If two trains of length a metres and b metres are moving in opposite directions at u m/s and v m/s, then:
Relative speed of the trains =x+y(since they are moving in opp direction)
Total distance covered = L1+L2
So time taken to cross each other = total distance /relative speed
Hence 23=(27x+17y)/(x+y)
Sushma said:
2 decades ago
Thanks Ramakrishna, your answer is excellent.
Y.S.Rama Krishna said:
2 decades ago
Let the speeds of the two trains be x m/sec and y m/sec respectively.
Then, length of the first train = 27x metres,(length=speed*time..so length=x*27=27x metres)
and length of the second train = 17y metres.(length=speed*time..so length=y*17=17y metres)
If two trains of length a metres and b metres are moving in opposite directions at u m/s and v m/s, then:
The time taken by the trains to cross each other = (a + b)/u + v)sec.
By using above formula we get d solution for this.
Here it is given that they cross each other in 23 seconds.
So 23 = (27x+17y) / (x+y).
Then, length of the first train = 27x metres,(length=speed*time..so length=x*27=27x metres)
and length of the second train = 17y metres.(length=speed*time..so length=y*17=17y metres)
If two trains of length a metres and b metres are moving in opposite directions at u m/s and v m/s, then:
The time taken by the trains to cross each other = (a + b)/u + v)sec.
By using above formula we get d solution for this.
Here it is given that they cross each other in 23 seconds.
So 23 = (27x+17y) / (x+y).
Prabhakaran said:
2 decades ago
Im not clear with above step can anyone give more explanation about this problem. I have doubt in (27x+17y) / (x+y) =23 what this statement mean by. Anyone help me please.
Lokesh said:
2 decades ago
27x - 24x = 23y - 17y
4x = 6y
x/y = 3/2.
4x = 6y
x/y = 3/2.
Bhanu said:
2 decades ago
Take all x terms once side and why terms other side then subtract we get 4x = 6y.
Sameer said:
2 decades ago
Can anyone explain me how he got this step 4x = 6y ?
Sunny(sunil) said:
2 decades ago
http://www.indiabix.com/aptitude/problems-on-trains/formulas
Look at this link then you can understand why we use x+y down there!
Look at this link then you can understand why we use x+y down there!
Vivek said:
2 decades ago
How the (27x+17y)/x+y=23 formula comes?
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