Without stoppages, a train runs at 150 km/h; with stoppages, its average speed is 100 km/h. How many minutes per hour does the train stop?

Introduction / Context:
The average speed over a clock hour falls below the running speed if the train stops. Using distance equivalence over one hour gives the stoppage duration per hour.

Given Data / Assumptions:

• Running speed = 150 km/h
• Average speed = 100 km/h

Concept / Approach:
In one hour, actual distance = 100 km. Running time = distance / running speed = 100/150 h; stoppage = 1 − (100/150) h.

Step-by-Step Solution:

Verification / Alternative check:
Over 60 minutes: 40 minutes moving at 150 km/h gives 100 km average overall ✔

Why Other Options Are Wrong:

• 15, 25, 45 minutes would yield averages different from 100 km/h.

Common Pitfalls:

• Dividing 150 by 100 instead of 100 by 150 to get running-time fraction.

Final Answer:
20