Question

A car travelled 2 hours at 60 km/h and 100 km at 40 km/h. Please calculate the average speed of the car. Show your calculations (including the data, formulas, result and unit).

Answer 1

To calculate the average speed of the car, we first need to determine the total distance traveled and the total time taken.

### Step 1: Calculate the distances
1. **Distance covered in the first part**:
- Speed = 60 km/h
- Time = 2 hours
\[
\text{Distance}_1 = \text{Speed} \times \text{Time} = 60 \, \text{km/h} \times 2 \, \text{h} = 120 \, \text{km}
\]

2. **Distance covered in the second part**:
- Distance = 100 km (given)

### Step 2: Calculate the total distance
\[
\text{Total Distance} = \text{Distance}_1 + \text{Distance}_2 = 120 \, \text{km} + 100 \, \text{km} = 220 \, \text{km}
\]

### Step 3: Calculate the total time
1. **Time taken for the first part**: 2 hours (already given)
2. **Time taken for the second part**:
- Distance = 100 km
- Speed = 40 km/h
\[
\text{Time}_2 = \frac{\text{Distance}}{\text{Speed}} = \frac{100 \, \text{km}}{40 \, \text{km/h}} = 2.5 \, \text{h}
\]

### Step 4: Calculate the total time
\[
\text{Total Time} = \text{Time}_1 + \text{Time}_2 = 2 \, \text{h} + 2.5 \, \text{h} = 4.5 \, \text{h}
\]

### Step 5: Calculate the average speed
The average speed is calculated using the formula:
\[
\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}}
\]
\[
\text{Average Speed} = \frac{220 \, \text{km}}{4.5 \, \text{h}} \approx 48.89 \, \text{km/h}
\]

### Result
The average speed of the car is approximately **48.89 km/h**.