A car travels 75 km at 25 km/h, then 25 km at 5 km/h, and finally 50 km at 25 km/h along the same route. What is the overall average speed for the entire 150 km journey?

Introduction / Context:
Average speed equals total distance divided by total time, never the simple average of the listed speeds unless times or distances are equal in a specific way. Here, segment distances and speeds are given explicitly, making the computation direct by summing segment times and distances.

Given Data / Assumptions:

• Segment 1: 75 km at 25 km/h.
• Segment 2: 25 km at 5 km/h.
• Segment 3: 50 km at 25 km/h.

Concept / Approach:
Compute each segment’s time (distance/speed), add them to get total time. Sum distances to get total distance. Then average speed = total distance / total time.

Step-by-Step Solution:

Verification / Alternative check:
Weighted average by time produces the same value; the very slow 5 km/h segment dominates time.

Why Other Options Are Wrong:
25 or 40 km/h ignore the long slow segment; 12.5 km/h would require more than 10 h total time.

Common Pitfalls:
Taking the simple mean of 25, 5, 25, which is not applicable across unequal times.

Final Answer:
15 km/h