Maths question from Laboratory Attendant exam, 2026 by JKSSB
Two trains of lengths 120 m and 180 m are moving in opposite directions at 54 km/h and 72 km/h respectively. How long will they take to cross each other?
Last updated Jun 13, 2026
Correct Answer:
Option B —
9 sec
1. Find the total distance to cover
When two trains pass each other, they have to clear the combined length of both trains.
First train: 120 meters
Second train: 180 meters
Combined distance: 120 + 180 = 300 meters
2. Find their combined speed
Because the trains are driving toward each other, they close the gap much faster than a single train moving alone. To find their combined speed, we add their speeds together.
54 km/h + 72 km/h = 126 km/h
3. Change the speed to meters per second
Since our train lengths are measured in meters, we need to know how many meters the trains cover every second instead of every hour.
To convert 126 km/h into meters per second, you divide it by 3.6.
126 divided by 3.6 = 35 meters per second
4. Calculate the time
Now we know the trains need to cover a total of 300 meters, and they travel at a combined pace of 35 meters every single second.
300 meters divided by 35 meters per second equals roughly 8.57 seconds.
Rounding 8.57 seconds to the nearest whole option gives us 9 seconds.
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.
