Question

A man travels from town P to town Q at 30 km/h and returns along the same road at 60 km/h. What is his average speed for the whole journey?

• A. 40 km/h
• B. 45 km/h
• C. 48 km/h
• D. 50 km/h

Hint:

For equal distances use the harmonic mean, not the simple average.

Answer 1

The Correct Option is A

Step 1: Use the equal-distance average speed formula.
\[\text{Avg speed} = \dfrac{2ab}{a + b}\] with \(a = 30\), \(b = 60\).
Step 2: Substitute.
\[\dfrac{2 \times 30 \times 60}{30 + 60} = \dfrac{3600}{90} = \boxed{40 \text{ km/h}}\]