Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 13)
13.
Two trains, each 100 m long, moving in opposite directions, cross each other in 8 seconds. If one is moving twice as fast the other, then the speed of the faster train is:
Answer: Option
Explanation:
Let the speed of the slower train be x m/sec.
Then, speed of the faster train = 2x m/sec.
Relative speed = (x + 2x) m/sec = 3x m/sec.
 |
(100 + 100) | = 3x |
| 8 |
24x = 200
| x = |
25 | . |
| 3 |
| So, speed of the faster train = | 50 | m/sec |
| 3 |
| = |  |
50 | x | 18 |  km/hr |
| 3 | 5 |
= 60 km/hr.
Discussion:
74 comments Page 2 of 8.
Praveen Sharma said:
10 years ago
Here (100+100)/8 = 3x.
200/8 = 3x.
25 = 3x.
So x = 25/3 m/s it is speed of slow train.
We want speed of fast train, it is 2x where x = 25/2 m/s.
So speed of fast train = 2*25/3 m/s.
So 50/3 m/s.
And we convert in km/s using 18/5.
So (50*18)/(3*5) = 900/15 = 60 km/h.
200/8 = 3x.
25 = 3x.
So x = 25/3 m/s it is speed of slow train.
We want speed of fast train, it is 2x where x = 25/2 m/s.
So speed of fast train = 2*25/3 m/s.
So 50/3 m/s.
And we convert in km/s using 18/5.
So (50*18)/(3*5) = 900/15 = 60 km/h.
(1)
Roshan Kumar said:
4 years ago
Answer will be 30km/hr.
Because the simplification of 200/24 = 25/6.
But in the answer it's given as 25/3 that's why the answer is changed to 60 km/hr.
Because the simplification of 200/24 = 25/6.
But in the answer it's given as 25/3 that's why the answer is changed to 60 km/hr.
(1)
Nisha said:
4 years ago
How come 50/3? Please explain me.
(1)
Fabarah Israr said:
4 years ago
Can someone please tell me, we are already multiplying 2 with x then why we are again multiplying with 2 with 25/6? Please explain me.
(1)
Aashu said:
4 years ago
@Fabarah Israr.
It's not 25/6 it's 25/3.
And it is asked to calculate the speed of a faster train.
x= 25/3 (speed of the slower train)
whereas the speed of the faster train is 2x, therefore 2*25/3 gives 50/3.
It's not 25/6 it's 25/3.
And it is asked to calculate the speed of a faster train.
x= 25/3 (speed of the slower train)
whereas the speed of the faster train is 2x, therefore 2*25/3 gives 50/3.
(1)
Shiva said:
1 decade ago
Why you are all talking always 5/18 to convert kmph into m/sec, I can't understand that logic, please explain reason behind that. Thanks in advance.
Praveen Sharma said:
10 years ago
How come 3?
Answer - If speed of slow train is x km/h.
In question the speed of fast train is twice to slow train.
So speed of fast train = 2*(Speed of slow train).
So speed of fast train = 2*(x) = 2x.
If trains are moving in opposite direction then we ADD the Speed. And trains are in same direction then we sub speed.
Here train in same direction so we add the speed of both train.
So x + 2x = 3x.
Answer - If speed of slow train is x km/h.
In question the speed of fast train is twice to slow train.
So speed of fast train = 2*(Speed of slow train).
So speed of fast train = 2*(x) = 2x.
If trains are moving in opposite direction then we ADD the Speed. And trains are in same direction then we sub speed.
Here train in same direction so we add the speed of both train.
So x + 2x = 3x.
Sam said:
9 years ago
@Aditiyabala.
Super explanation, Thank you.
Super explanation, Thank you.
Jai said:
9 years ago
If 1st train accelerated by 0.3 and 2nd 0.2 then how to solve it?
Vijay arun said:
9 years ago
@Ikram.
Nice explanation.
Nice explanation.
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