A bus runs at 54 km/h while moving and averages 45 km/h overall when stoppages are included. How many minutes per hour does the bus stop?

Introduction / Context:
Overall average speed with stoppages equals distance covered in one whole hour divided by one hour. If the running speed is higher, the bus must have stopped for some portion of the hour.

Given Data / Assumptions:

• Running speed = 54 km/h (no stops).
• Overall speed including stops = 45 km/h.
• Assume constant running speed whenever moving.

Concept / Approach:
Let moving time per hour be t hours. Then distance in 1 clock-hour is 54*t. Since average is 45 km/h, we have 54*t = 45, giving t. Stoppage time = 60 minutes * (1 - t).

Step-by-Step Solution:

Verification / Alternative check:
Distance in 50 minutes at 54 km/h is 45 km, matching the overall hourly average.

Why Other Options Are Wrong:
9 or 12 minutes are close distractors but do not satisfy 54*t = 45; 20 and 8 minutes deviate further.

Common Pitfalls:
Confusing average of speeds with time-weighted average; the bus’s average depends on time moving vs. stopped.

Final Answer:
10 minutes