Calculation of Average Speed

To calculate the average speed for the whole journey, we need to consider the total distance traveled and the total time taken. The average speed can be calculated using the formula:

Average Speed = Total Distance / Total Time

Step 1: Calculate the total distance
The car travels 100 km in one direction and then returns the same distance, resulting in a total distance of 200 km.

Step 2: Calculate the total time
The time taken for the first part of the journey can be calculated using the formula:

Time = Distance / Speed

For the first part of the journey, the distance is 100 km and the speed is 60 km per hour. Plugging these values into the formula, we get:

Time = 100 km / 60 km/h = 1.67 hours

Similarly, for the return journey, the time taken can be calculated as:

Time = 100 km / 40 km/h = 2.5 hours

The total time for the whole journey is the sum of the time taken for both parts:

Total Time = 1.67 hours + 2.5 hours = 4.17 hours

Step 3: Calculate the average speed
Now that we have the total distance (200 km) and the total time (4.17 hours), we can calculate the average speed using the formula:

Average Speed = Total Distance / Total Time

Average Speed = 200 km / 4.17 hours ≈ 48 km/h

Therefore, the average speed for the whole journey is approximately 48 km per hour.

Conclusion
The average speed for the whole journey, considering a car traveling 100 km at a speed of 60 km per hour and returning at a speed of 40 km per hour, is approximately 48 km per hour. It is important to note that the average speed is different from the average of the two speeds.