Understanding Average Speed Calculation

The question asks for the average speed of the truck driver over the entire journey. Average speed is defined as the total distance traveled divided by the total time taken for the journey.

The formula for average speed is:

$$ \text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}} $$

To find the average speed, we need to calculate the total distance traveled and the total time spent, including any rest periods.

Step-by-Step Calculation

1. Calculate Distance for the First Part of the Journey

The driver drove for 4 hours at a speed of 40 km/h.

Using the formula: Distance = Speed × Time

Distance 1 = $ 40 \text{ km/h} \times 4 \text{ h} $

Distance 1 = $ 160 \text{ km} $

2. Account for the Rest Period

The driver rested for 1 hour. During this time, the distance traveled is 0 km.

Rest Time = $ 1 \text{ h} $

3. Calculate Distance for the Second Part of the Journey

After the rest, the driver drove for 3 hours at a speed of 50 km/h.

Distance 2 = $ 50 \text{ km/h} \times 3 \text{ h} $

Distance 2 = $ 150 \text{ km} $

4. Calculate Total Distance Traveled

Total Distance = Distance 1 + Distance 2

Total Distance = $ 160 \text{ km} + 150 \text{ km} $

Total Distance = $ 310 \text{ km} $

5. Calculate Total Time Taken for the Journey

Total Time = Time for first part + Rest Time + Time for second part

Total Time = $ 4 \text{ h} + 1 \text{ h} + 3 \text{ h} $

Total Time = $ 8 \text{ h} $

6. Calculate the Average Speed

Now, apply the average speed formula:

Average Speed = $ \frac{\text{Total Distance}}{\text{Total Time}} $

Average Speed = $ \frac{310 \text{ km}}{8 \text{ h}} $

Average Speed = $ 38.75 \text{ km/h} $

Conclusion

The driver's average speed during the whole journey was 38.75 km/h.