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:
239 comments Page 8 of 24.
Jagadeesh said:
2 decades 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:
10 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:
9 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.
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!
Kaviarasan said:
9 years ago
Simple method:
A B
27 17
23 (Common time for A & B)
6 4
(23-17) (27-23)
3 : 2
A B
27 17
23 (Common time for A & B)
6 4
(23-17) (27-23)
3 : 2
Shivam Mehta said:
7 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.
Ramhari said:
8 years ago
In this question, there is no any data that two trains are equal length. A train has passed a man in 27 seconds and another has passed in 17. The second one might be faster or short in length. So, Both can happen.
Ebe said:
5 years ago
I have a small doubt regarding the formula.
In the question, they have said to find the ratio of speed. Not the ratio of time.
So aren't we supposed to modify the formula accordingly? Please someone explain.
In the question, they have said to find the ratio of speed. Not the ratio of time.
So aren't we supposed to modify the formula accordingly? Please someone explain.
(11)
Pankj said:
9 years ago
One doubt.
According to this answer train taking 27 sec to cross the man having more speed than train taking 17 sec. As per my knowledge train taking more time having less speed anyone can explain this ?
According to this answer train taking 27 sec to cross the man having more speed than train taking 17 sec. As per my knowledge train taking more time having less speed anyone can explain this ?
Rajkumar said:
1 decade ago
Dear friend cherry the logic is very simple to understand we know speed = distance/time in this way 27 is the time of one train to pass a man and "x"is the assuming speed I hope to you may be understand.
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