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:
234 comments Page 15 of 24.
Soniya said:
1 decade ago
This is very good method to understand.
Prasanth said:
1 decade ago
Can anyone please tel me how x+y is came.
They asked to find speed of that we have to use speed = length\time only know but how x+y is came.
They asked to find speed of that we have to use speed = length\time only know but how x+y is came.
Racha manish said:
1 decade ago
Let we have to assume those to get ratio of that speeds.
Gaurav singh said:
1 decade ago
Time x speed = distance.
Let the speeds of two train be x and y.
Then distances will be 27x for 1st train.
17y for 2nd train.
Now when they both cross each other fully. Time is 23 seconds.
Distance will be length of 1st train + length of 2nd train.
Speed will be as we assumed above is x and y (sum of both the speed).
So,
23 = (27x+17y)/x+y.
23(x+y) = 27x+17y.
23y-17y = 27x-23x.
6y = 4x.
3y = 2x.
Hence the answer 3:2.
Let the speeds of two train be x and y.
Then distances will be 27x for 1st train.
17y for 2nd train.
Now when they both cross each other fully. Time is 23 seconds.
Distance will be length of 1st train + length of 2nd train.
Speed will be as we assumed above is x and y (sum of both the speed).
So,
23 = (27x+17y)/x+y.
23(x+y) = 27x+17y.
23y-17y = 27x-23x.
6y = 4x.
3y = 2x.
Hence the answer 3:2.
James said:
1 decade ago
Can someone please explain to me how 27x+17y = 23x + 23y & 4x + 6y?
Sharad said:
1 decade ago
@James.
27x+17y = 23x+23y.
27x-23x = 23y-17y.
4x = 6y.
4x/2 = 6y/2.
2x = 3y.
x/y = 3/2.
27x+17y = 23x+23y.
27x-23x = 23y-17y.
4x = 6y.
4x/2 = 6y/2.
2x = 3y.
x/y = 3/2.
Adi said:
1 decade ago
Short cut:
T2 = 23-17 = 6.
T1 = 27-23 = 4.
S1/S2 = T2/T1.
= 6/4 = 3/2.
T2 = 23-17 = 6.
T1 = 27-23 = 4.
S1/S2 = T2/T1.
= 6/4 = 3/2.
Vincent said:
1 decade ago
Let the speeds of the two trains be x m/sec and why m/sec respectively.
Reference to man standing on the platform.
Length of the first train = 27X metres,
Length of the second train = 17Y metres.
Total speed of train when crossing opposite direction is (x+y) m/s.
Two trains are crossing each other in 23 seconds.
So length of two trains using this condition is (x+y) 23 m.
So 27X+17Y = 23X+23Y.
4X = 6Y.
X/Y = 3/2.
Reference to man standing on the platform.
Length of the first train = 27X metres,
Length of the second train = 17Y metres.
Total speed of train when crossing opposite direction is (x+y) m/s.
Two trains are crossing each other in 23 seconds.
So length of two trains using this condition is (x+y) 23 m.
So 27X+17Y = 23X+23Y.
4X = 6Y.
X/Y = 3/2.
Rashmi said:
1 decade ago
Why is time considered as a distance or length. As per the question it is 27 seconds and 17 seconds? I see through out the discussion we consider seconds in meters. Could anyone clear my doubt please?
Sumitra said:
1 decade ago
Here the time taken by two trains itself 27 & 17 sec rt.
So we know the formula that speed=d/t. Let us take the speed of the two trains is x & y.
Then the corresponding distances are 27x and 17y.
Then t=d/s as per formula.
Time taken to cross each other is 23 sec.
Equate that time as 23 sec and to cross that man by both trains.
i.e (27x+17y)/(x+y) = 23.
Then solve the equation we will get the answer.
So we know the formula that speed=d/t. Let us take the speed of the two trains is x & y.
Then the corresponding distances are 27x and 17y.
Then t=d/s as per formula.
Time taken to cross each other is 23 sec.
Equate that time as 23 sec and to cross that man by both trains.
i.e (27x+17y)/(x+y) = 23.
Then solve the equation we will get the answer.
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