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 7 of 8.
Priyesh Jain said:
1 decade ago
"D = ST".
Total distance = 100+100 = 200 m.
Relative speed = s+2s = 3s.
T= 8 sec.
Putting these values.
200 = 3s*8.
S = 200/8*3.
S = 25/3 m/s.
Now be need to calculate speed in terms of km/h.
25/3*18/5 = 30 km/h.
Speed of slower train now speed of faster train is 60 km/h that is just double.
Total distance = 100+100 = 200 m.
Relative speed = s+2s = 3s.
T= 8 sec.
Putting these values.
200 = 3s*8.
S = 200/8*3.
S = 25/3 m/s.
Now be need to calculate speed in terms of km/h.
25/3*18/5 = 30 km/h.
Speed of slower train now speed of faster train is 60 km/h that is just double.
Sudha said:
1 decade ago
I did not understand how you got 50/3? Please I need a clear explanation.
Studybeforexam said:
1 decade ago
25/3 + 25/3 = 50/3 i.e. 3 being a common denominator.
Mounika said:
1 decade ago
What 50/3 I didn't understand this step?
Swetha said:
1 decade ago
Hi @Raja,
5/18 is to convert KM to Meters.
18/5 is to convert Meters to KM.
As, in question it is given in Meters but answer is in meters so have to convert Meters to KM. So we are using.
5/18 is to convert KM to Meters.
18/5 is to convert Meters to KM.
As, in question it is given in Meters but answer is in meters so have to convert Meters to KM. So we are using.
Rajaprabu said:
1 decade ago
What is 18/5 and 5/18 ? why we are using please explain?
Khumalo said:
1 decade ago
Where is 3 coming from?
Charmi said:
1 decade ago
How did you reversed the 18/5 and multiplied with 50/3?
Divya said:
1 decade ago
Here there is no need of finding relative speed right? then why we find relative speed?
Thenmolzhi said:
1 decade ago
Relative speed = (x+y);
x = x;
y = Twice faster than 'x', So 2x;
y = 2x;
Relative speed = (x+2x) = 3x.
x = x;
y = Twice faster than 'x', So 2x;
y = 2x;
Relative speed = (x+2x) = 3x.
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers