A car travels in three stages: • 30 min at 40 km/h, • 45 min at 60 km/h, • 2 h at 70 km/h. What is the car’s average speed over the entire journey (in km/h)?

Introduction / Context:
Average speed over multiple segments with different speeds equals total distance divided by total time, not the simple average of speeds. Convert each stage to hours, compute distances, sum, then divide by the total time.

Given Data / Assumptions:

• Stage 1: 0.5 h at 40 km/h.
• Stage 2: 0.75 h at 60 km/h.
• Stage 3: 2 h at 70 km/h.

Concept / Approach:
Total distance = Σ(v * t). Total time = 0.5 + 0.75 + 2 = 3.25 h. Average speed = total distance / 3.25.

Step-by-Step Solution:

Verification / Alternative check:
Weighted average by time yields the same result; simple mean of speeds would be incorrect.

Why Other Options Are Wrong:
58/67/71 km/h do not match total distance over total time.

Common Pitfalls:
Averaging speeds arithmetically without weighting by time intervals.

Final Answer:
63 km/h