Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 27)
27.
A train overtakes two persons who are walking in the same direction in which the train is going, at the rate of 2 kmph and 4 kmph and passes them completely in 9 and 10 seconds respectively. The length of the train is:
Answer: Option
Explanation:
| 2 kmph = |  |
2 x | 5 |  |
m/sec = | 5 | m/sec. |
| 18 | 9 |
| 4 kmph = | |
4 x | 5 | |
m/sec = | 10 | m/sec. |
| 18 | 9 |
Let the length of the train be x metres and its speed by y m/sec.
| Then, |  |
x |  |
= 9 and | |
x | |
= 10. |
|
|
9y - 5 = x and 10(9y - 10) = 9x
9y - x = 5 and 90y - 9x = 100.
On solving, we get: x = 50.
Length of the train is 50 m.
Discussion:
106 comments Page 11 of 11.
Raksha said:
5 years ago
I did not get it properly. Could someone explain me briefly?
Sumit said:
5 years ago
@Ramya.
Why don't you use x-4 equation?
Why don't you use x-4 equation?
Pooja said:
5 years ago
@All.
Why they do not subtract speed first, then convert into m/sec?
Can anyone explain, please?
Why they do not subtract speed first, then convert into m/sec?
Can anyone explain, please?
Nisma said:
5 years ago
There is a simple formula to do this type of questions.
If a train covers 2 persons with speed S1 and S2 in time T1 and T2, then the length of train is:
(S1-S2 ÷ T1-T2) * T1 * T2.
So applying it in this question;
{(4-2)5/18÷10-9} * 10 * 9 =50m.
Note:(4-2) is multiplied by 5/18 so as to convert km to m.
If a train covers 2 persons with speed S1 and S2 in time T1 and T2, then the length of train is:
(S1-S2 ÷ T1-T2) * T1 * T2.
So applying it in this question;
{(4-2)5/18÷10-9} * 10 * 9 =50m.
Note:(4-2) is multiplied by 5/18 so as to convert km to m.
Anand K said:
4 years ago
Treat both people separately.
1st compare person A(2 kmph) and train.
Speed = dist/time.
hence time = dist/speed.
Time(for A) = 9s.
Dist = length of train
Speed = relative speed btw A and train=(S-5/9)
S = speed of the train.
9 = LOT/(S-5/9) //LOT=Length of train.
Apply same for person B.
10=LOT/(S-10/9).
solve both equations and get;
LOT= 50mtrs.
1st compare person A(2 kmph) and train.
Speed = dist/time.
hence time = dist/speed.
Time(for A) = 9s.
Dist = length of train
Speed = relative speed btw A and train=(S-5/9)
S = speed of the train.
9 = LOT/(S-5/9) //LOT=Length of train.
Apply same for person B.
10=LOT/(S-10/9).
solve both equations and get;
LOT= 50mtrs.
Vivek Tiwari said:
4 weeks ago
@All.
Just, let the length of train = x, then find the speed of the train after that equals the relative speed of person and the relative sped of the train.
Just, let the length of train = x, then find the speed of the train after that equals the relative speed of person and the relative sped of the train.
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