Question

A car travels from A to B at 60 km/h and returns at 40 km/h. What is the average speed?

• A. 48 km/h
• B. 50 km/h
• C. 52 km/h
• D. 45 km/h

Hint:

Use \( \frac{2 \cdot s_1 \cdot s_2}{s_1 + s_2} \) for average speed over equal distances.

Answer 1

The Correct Option is A

We need the average speed for the round trip.
- Step 1: Average speed = \( \frac{\text{Total distance}}{\text{Total time}} \).
- Step 2: Distance A to B = \( d \). Total distance = \( 2d \).
- Step 3: Time: A to B = \( \frac{d}{60} \), B to A = \( \frac{d}{40} \). Total time = \( \frac{d}{60} + \frac{d}{40} = \frac{5d}{120} = \frac{d}{24} \).
- Step 4: Average speed = \( \frac{2d}{\frac{d}{24}} = 48 \) km/h.
- Step 5: Options:
- (a) 48: Correct.
Thus, the answer is a.