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:
75 comments Page 2 of 8.
Sudha said:
1 decade ago
When you divide 200/24, you won't get 25/3? So I request you to explain me properly.
(1)
Sarang said:
8 years ago
Distance =speed *time,
100+100=speed*8.
200=speed *8,
Speed=200/8,
Speed =25m/s,
Converting m/s into km/h.
25*18/5=90km/h,
As we want twice speed so first find single speed.
1+2 one is the speed of first train and 2 twice a second so combing we get 3 now,
Speed =90/3=30.
Now twice speed is 60km/h.
100+100=speed*8.
200=speed *8,
Speed=200/8,
Speed =25m/s,
Converting m/s into km/h.
25*18/5=90km/h,
As we want twice speed so first find single speed.
1+2 one is the speed of first train and 2 twice a second so combing we get 3 now,
Speed =90/3=30.
Now twice speed is 60km/h.
(1)
Praveen Sharma said:
1 decade 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:
6 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)
Fabarah Israr said:
5 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)
R.Rakesh KUmar said:
9 years ago
@Navin.
In question they have mentioned to calculate the speed of faster train i.e to calculate 2X
X=25/3 is the speed of the slower train and ( " If one is moving twice as fast the other" given in question).
2 * X = 2 * 25/3 => 50/3.
In question they have mentioned to calculate the speed of faster train i.e to calculate 2X
X=25/3 is the speed of the slower train and ( " If one is moving twice as fast the other" given in question).
2 * X = 2 * 25/3 => 50/3.
Sunil bhanovath said:
8 years ago
@Nutan.
Why 50/3 taken as speed of the train is 2x so that's why we should take.
Why 50/3 taken as speed of the train is 2x so that's why we should take.
Sonam said:
9 years ago
@Adityabala.
Nice explanation. Thanks.
Nice explanation. Thanks.
Navin said:
10 years ago
x = 25/3
So, speed of the faster train = 50/3 m/sec.
I can't understand these steps please help me.
So, speed of the faster train = 50/3 m/sec.
I can't understand these steps please help me.
K.ratnababu said:
9 years ago
This is another way.
two trains opposite direction 100m+100m=200m.
200m to cover 8 seconds then,
(200m 8sec
? 3600sec
90000m that means 90k).
3600sec that mean 1 hour to cover 90000m that is 90k/h.
the train speed is 2:1.
total 3 parts.
3parts 90kilometers then,
2parts ?
60k.
two trains opposite direction 100m+100m=200m.
200m to cover 8 seconds then,
(200m 8sec
? 3600sec
90000m that means 90k).
3600sec that mean 1 hour to cover 90000m that is 90k/h.
the train speed is 2:1.
total 3 parts.
3parts 90kilometers then,
2parts ?
60k.
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