Solution

Train Collision Problem

Navjivan Express leaves Ahmedabad at 6:30 am traveling at 50 km/h towards Baroda (100 km away).
At 7:00 am, Howrah-Ahmedabad Express leaves Baroda towards Ahmedabad at 40 km/h.
At 7:30 am, Mr. Shah realizes both trains are on the same track heading toward each other.

Navjivan distance by 7:30 am = 50 km/h × 1 h = 50 km
Howrah distance by 7:30 am = 40 km/h × 0.5 h = 20 km
Distance between trains at 7:30 am = 100 − (50 + 20) = 30 km
Relative speed = 50 + 40 = 90 km/h
Time until collision = 30 km / 90 km/h = 1/3 hour = 20 minutes

Time to avert collision: 20 minutes