Two trains leave New Delhi at the same time on straight tracks. One goes due North at 60 km/h; the other goes due South at 40 km/h. After how many hours will they be 150 km apart?

Introduction / Context:
When two trains move in opposite directions from the same point, separation grows at the sum of their speeds. Time to reach a given separation = separation / (sum of speeds).

Given Data / Assumptions:

• Speeds: 60 km/h northbound; 40 km/h southbound.
• Desired separation: 150 km.

Concept / Approach:
Sum speed = 60 + 40 = 100 km/h. Time = 150 / 100 = 1.5 h.

Step-by-Step Solution:

Verification / Alternative check:
After 1.5 h: distances 90 km and 60 km; separation 150 km.

Why Other Options Are Wrong:
4/3 and 3/4 h yield separations ≠ 150 km; 15/2 h is far too long.

Common Pitfalls:
Subtracting speeds instead of adding for diverging paths.

Final Answer:
3/2 h