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 9 of 11.
Swapnil said:
8 years ago
Awesome, thank you @Mancy.
Nitesh Mittal said:
7 years ago
2*9=18
4*10=40
10-9=1
Speed of train =(40-18)/1
Speed of train =22 km/hr
Now,
Length of train = (22-2) *(5/18) *9.
= 20*5/2,
= 50 mins.
4*10=40
10-9=1
Speed of train =(40-18)/1
Speed of train =22 km/hr
Now,
Length of train = (22-2) *(5/18) *9.
= 20*5/2,
= 50 mins.
Jaga said:
7 years ago
Please explain @Nitesh Mittal.
Nikky said:
7 years ago
Good explanation. Thanks @Amit.
Suraj said:
7 years ago
Please tell me that, where did the 5/18 come from?
Erram saicharan said:
7 years ago
Why y is considered as m/s?
Please explain that.
Please explain that.
Surbhi said:
7 years ago
Let the speed of train is x.
Then (x-2)9=(x-4)10.
9x-18=10x-40,
X=22.
Now let the length of the train is L.
L/(22-2)5/18=9,
So, L=50.
Then (x-2)9=(x-4)10.
9x-18=10x-40,
X=22.
Now let the length of the train is L.
L/(22-2)5/18=9,
So, L=50.
VamC said:
7 years ago
Why we should consider y-5/9 and y-10/9 in Denominators (Speed) ?
Ronie said:
7 years ago
@Vamc.
You need to convert the 2kmph and 4kmph to mps. So on converting it gives 5/9 m/s and 10/9m/s.
According to the formula for the same direction movement: (speed of train -speed of man).
As the speed of man is slow.
You need to convert the 2kmph and 4kmph to mps. So on converting it gives 5/9 m/s and 10/9m/s.
According to the formula for the same direction movement: (speed of train -speed of man).
As the speed of man is slow.
Ronie said:
7 years ago
You first solve for y which will give y=55/9m/s now convert it into km/h which will be 22km/h
But the actual speed of the train is:
(22-2)km/h=20km/h
2km/h is the speed of the 1st person
20km/h is 50/9 m/s when you convert
Now as we know,
Length of train = speed * time.
So, L=(50/9)*9,
or, L=50m.
Go through the formula how to convert kmph to mps. Because when it is given in seconds you have to convert it to mph.
But the actual speed of the train is:
(22-2)km/h=20km/h
2km/h is the speed of the 1st person
20km/h is 50/9 m/s when you convert
Now as we know,
Length of train = speed * time.
So, L=(50/9)*9,
or, L=50m.
Go through the formula how to convert kmph to mps. Because when it is given in seconds you have to convert it to mph.
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