Two cities A and B are 360 km apart. A car goes from A to B with a speed of 40 km/hr and returns to A with a speed of 60 km/hr. What is the average speed of the car?

The correct answer is B) 48 km/hr.

Explanation: To calculate the average speed, we use the formula: Average Speed = Total Distance / Total Time.

1. Calculate the time taken for the journey from A to B: Time (A to B) = Distance / Speed = 360 km / 40 km/hr = 9 hours.

2. Calculate the time taken for the journey from B to A: Time (B to A) = Distance / Speed = 360 km / 60 km/hr = 6 hours.

3. Calculate the Total Distance travelled: Total Distance = Distance (A to B) + Distance (B to A) = 360 km + 360 km = 720 km.

4. Calculate the Total Time taken: Total Time = Time (A to B) + Time (B to A) = 9 hours + 6 hours = 15 hours.

5. Calculate the Average Speed: Average Speed = Total Distance / Total Time = 720 km / 15 hours = 48 km/hr.

Alternatively, for a round trip with equal distances and different speeds (v1 and v2), the average speed can be calculated using the harmonic mean formula: Average Speed = (2 * v1 * v2) / (v1 + v2). Average Speed = (2 * 40 * 60) / (40 + 60) = (2 * 2400) / 100 = 4800 / 100 = 48 km/hr.

Analysis of Options: A) 45 km/hr: Incorrect. B) 48 km/hr: Correct, as calculated. C) 50 km/hr: This is the simple arithmetic mean of the two speeds ((40+60)/2), which is incorrect for average speed when the time taken for each part of the journey is different. D) 55 km/hr: Incorrect.