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 10 of 24.
Arifshaikh said:
9 years ago
Try the rule of alligation.
It will take 30 sec.
It will take 30 sec.
Sarat said:
9 years ago
TIME = DISTANCE /SPEED.
We don't know how much distance apart
27x is train1 distance at which it crosses man
17y is 2nd train.
We know when they meet 23 sec.
23 = 27x + 17y/ x + y.
We don't know how much distance apart
27x is train1 distance at which it crosses man
17y is 2nd train.
We know when they meet 23 sec.
23 = 27x + 17y/ x + y.
Shrikant said:
9 years ago
@Narayan.
Your answer is good it is a bit easy method.
Your answer is good it is a bit easy method.
Heisenberg said:
9 years ago
Thanks @Narayan.
=> Guys use the method of mixture and allegation the answer is very much easy.
=> Guys use the method of mixture and allegation the answer is very much easy.
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.
Mukesh said:
9 years ago
Total distance / total speed = total time.
This is the simple solution (X + Y) = relative speed.
Trains comes towards each other.
This is the simple solution (X + Y) = relative speed.
Trains comes towards each other.
Smnk said:
9 years ago
Guys!
Difference between the 23s and 27s is 4 and,
Difference between the 23s and 17s is 6 of other train.
So, the ratio is 4 and 6.
Difference between the 23s and 27s is 4 and,
Difference between the 23s and 17s is 6 of other train.
So, the ratio is 4 and 6.
Raj said:
9 years ago
Short-cut : Alligation method.
27 17
23
6 4
= 6 : 4 means 3 : 2 => Answer.
27 17
23
6 4
= 6 : 4 means 3 : 2 => Answer.
Vinod reddy said:
9 years ago
Here is the formula when two trains crosses each other,
s1 + s2 = l1 + l2/time.
According to the problem.
x + y = (27x + 17y) /23.
27x + 17y = (x + y)23.
x/y = 3/2.
s1 + s2 = l1 + l2/time.
According to the problem.
x + y = (27x + 17y) /23.
27x + 17y = (x + y)23.
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.
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