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 7 of 11.
Farooqui mehtab said:
8 years ago
let x be the speed of train;
(x-2) *(5/18) *9 = (x-4) *(5/18) *10
9x-18 = 10x-40
x = 22 m/sec.
Now, substitute this in,
Length of train = (x-2) *(5/18) *9,
= (22-2) *(5/18) *9 = 20*5/2,
= 50 mins.
(x-2) *(5/18) *9 = (x-4) *(5/18) *10
9x-18 = 10x-40
x = 22 m/sec.
Now, substitute this in,
Length of train = (x-2) *(5/18) *9,
= (22-2) *(5/18) *9 = 20*5/2,
= 50 mins.
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.
Erram saicharan said:
7 years ago
Why y is considered as m/s?
Please explain that.
Please explain that.
Suraj said:
7 years ago
Please tell me that, where did the 5/18 come from?
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
@Mancy
Check your equation.
You wrote : 9y = 5+x.
y = 5+x/9. This is not possible you have divided x by 9 but haven't divided 5 by 9.
It would be y=5/9+ x/9.
Check your equation.
You wrote : 9y = 5+x.
y = 5+x/9. This is not possible you have divided x by 9 but haven't divided 5 by 9.
It would be y=5/9+ x/9.
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