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:
237 comments Page 14 of 24.
Harish said:
1 decade ago
I have solved it in yet simple(crude) way.
Don't worry about their crossing each other in 23 seconds or whatever.
On the face of it, one can make out that he has asked the simplified ration for 27:17.
Simply take them to next higher level so that both of them are divisible by common highest divisor.
i.e. 30/20 = 3/2.
(but recommended not to follow it, as it doesn't apply to every problem?).
Don't worry about their crossing each other in 23 seconds or whatever.
On the face of it, one can make out that he has asked the simplified ration for 27:17.
Simply take them to next higher level so that both of them are divisible by common highest divisor.
i.e. 30/20 = 3/2.
(but recommended not to follow it, as it doesn't apply to every problem?).
SWETHA.T said:
1 decade ago
SPEED = DISTANCE/TIME.
DISTANCE/SPEED = TIME.
i.e 27X+17Y/X+Y = 23.
DISTANCE/SPEED = TIME.
i.e 27X+17Y/X+Y = 23.
Het said:
1 decade ago
@Arashan has describe very well with formula of speed.
Sarath said:
1 decade ago
Lets assume,
The train 1 speed= x m/sec ==> distance traveled by the train 1= 27*x m.
Similarly assume the speed of the train 2 is y m/sec then the train 2 has traveled a distance of 17*y meter.
The total distance (x+y)*23 m.
Therefore,
23(x+y) = 27x+17y.
23x+23y=27x+17y.
==> 4x=6y.
==> x/y=3/2.
Therefore x:y= 3:2. Answer B.
The train 1 speed= x m/sec ==> distance traveled by the train 1= 27*x m.
Similarly assume the speed of the train 2 is y m/sec then the train 2 has traveled a distance of 17*y meter.
The total distance (x+y)*23 m.
Therefore,
23(x+y) = 27x+17y.
23x+23y=27x+17y.
==> 4x=6y.
==> x/y=3/2.
Therefore x:y= 3:2. Answer B.
Vivek Kumar said:
1 decade ago
Hey if we follow the physics concept then relative distance should decrease while crossing each other. Then it should be (27x - 17y)/(x+y). Isn't it?
Vadivel said:
1 decade ago
Why should both trains have different length. Even sometimes they can have same length and can run in different speeds right. Then how can we do like that. Can anyone explain please?
Krishna said:
1 decade ago
If I divide speed of one train 27 divided by another its almost 1.5 can I choose 3:2. Is it a pure coincidence ?
Amit Jana said:
1 decade ago
#Krishna no this is not possible as you say. Then cross each other in 23 sec. Is have no sense?
Amit Jana said:
1 decade ago
#Vivek kumar.
Here the questions is : two train of length a and b are run in opposite directions at u m/sec. and v m/sec., then the time taken by the trains to cross each other = (a+b)/(u+v).
And if two train of length a and b are run in same directions at u m/sec. and v m/sec., then the time taken by the faster trains to cross the slower train = (a+b)/(u-v)
Here the questions is : two train of length a and b are run in opposite directions at u m/sec. and v m/sec., then the time taken by the trains to cross each other = (a+b)/(u+v).
And if two train of length a and b are run in same directions at u m/sec. and v m/sec., then the time taken by the faster trains to cross the slower train = (a+b)/(u-v)
Srinivasa raju said:
1 decade ago
Total Distance/Total Speed = Total Time;
27X+17Y/X+Y = 23.
27X+17Y/X+Y = 23.
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