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 7 of 24.
Sachin kamble said:
1 decade ago
According to my opinion the first train crosses the man after crossing the other train i.e. 4 sec late and second train will crosses the man 6 sec earliar before it cross the other train .
Just take the ratio of 6:4 we get 3:2 i.e speed of seocnd train:speed of first train.
Just take the ratio of 6:4 we get 3:2 i.e speed of seocnd train:speed of first train.
Confused said:
1 decade ago
Sorry guys for pecking on the same thing again.
But Why is it necessary that total distance covered = sum of the train's length?
Isn't the above question assuming that before the collision both trains are travelling the distance only equal its own length.
But Why is it necessary that total distance covered = sum of the train's length?
Isn't the above question assuming that before the collision both trains are travelling the distance only equal its own length.
Karthik said:
1 decade ago
Velocity = distance/time.
Let velocities are x, y m/s.
x = d1/27; y = d2/17;
d1 = 27x; d2 = 17y;
Step 2: According to relative speed, since they are running in opposite direction their speeds are added.
x+y = d1+d2/23.
Sub d1 and d2; find answer.
Let velocities are x, y m/s.
x = d1/27; y = d2/17;
d1 = 27x; d2 = 17y;
Step 2: According to relative speed, since they are running in opposite direction their speeds are added.
x+y = d1+d2/23.
Sub d1 and d2; find answer.
Yogender prashad said:
1 decade ago
Let the speed of the train is Xm/s & Ym/s resp.
accordingto the qus.
27x meter is the speed of the first train
17x " " " second "
finally both the the train meet =23(x+y)
27x+17y=23(x+y)
4x=6y
x/y=3/2
accordingto the qus.
27x meter is the speed of the first train
17x " " " second "
finally both the the train meet =23(x+y)
27x+17y=23(x+y)
4x=6y
x/y=3/2
Shekharsa said:
1 decade ago
When two train s of a length a and b, of speed u, v m/sec.they move to cross each other. Time taken by the two trains cross each other is a+b(u+v). Because of these formula we have find the length of trains. I hope understood these problem.
P S said:
9 years ago
Another approach by looking at answers, in question, 27 come first and 17 come later so in answer bigger number will come first and smaller later, that option is "B" only, so we can find answer without going for actual calculation.
Kiran g said:
9 years ago
I have another method mixture alligation.
17 27
23
? ?
(27-23) (23-17)
4 6
Answer is 2:3.
17 27
23
? ?
(27-23) (23-17)
4 6
Answer is 2:3.
Jagadeesh said:
1 decade ago
Hi priya u can do like this take speed of train A is x and speed of B is Y
x(take difference between speed of train A and crossing time)=y(take difference between train B and crossing time) i.e
x(27-23)=y(23-17)
4x=6y
x/y=3/2
x(take difference between speed of train A and crossing time)=y(take difference between train B and crossing time) i.e
x(27-23)=y(23-17)
4x=6y
x/y=3/2
Kiran Kumar said:
9 years ago
This can be easily done by the method of allegations.
27 17
23
(23-17) : (27-23)
6 : 4
3 : 2
Or by weighted average,
S1/S2 = (23-17)/(27-23)
=> 3/2 and that is the required ratio.
27 17
23
(23-17) : (27-23)
6 : 4
3 : 2
Or by weighted average,
S1/S2 = (23-17)/(27-23)
=> 3/2 and that is the required ratio.
Ajay said:
8 years ago
We know time=distance/speed,
The first train length = 27x and second train length=17y.
Given that two trains will cross each other in 23 sec,so applying t=d/s formula.
23 = total distance/total speed.
=> 23=27x+17y/x+y.
The first train length = 27x and second train length=17y.
Given that two trains will cross each other in 23 sec,so applying t=d/s formula.
23 = total distance/total speed.
=> 23=27x+17y/x+y.
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