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 6 of 8.
Garvit said:
8 years ago
Why wasn't the speed of one train 1 considered x and other considered y? Why we're both taken as x?
Sarang said:
7 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)
Eudis said:
7 years ago
From where did 18/5 come? Please explain me.
Reeha said:
7 years ago
@Eudis.
It's the basic conversion principle, From km/hr to m/s we can use 5/18 and the reciprocal for vice versa.
It's the basic conversion principle, From km/hr to m/s we can use 5/18 and the reciprocal for vice versa.
Ganesh said:
7 years ago
Consider one train x speed and another one is x one twice speed to the other train then x+2x-3x.
Nutan said:
7 years ago
(50/3) * (18/3) = 60 how?
Sunil bhanovath said:
7 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.
Sowdi said:
7 years ago
Thanks for your explanation @Sarang.
Punam said:
6 years ago
How come 50/3?
Manivel said:
6 years ago
@Punam.
Substitute the X value in faster train 2X, 2* (25/3) =50/3. M.
Substitute the X value in faster train 2X, 2* (25/3) =50/3. M.
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