Execise 21 1) A truck travels at an average speed of $$ 70 \mathrm{~km} / \mathrm{h} $$. a) If the truck travels a distance of 420 km from Johannesburg to Pietermaritzburg, how long will the jo take? b) What speed would the truck have to travel at to make the journey in 3 hours?

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Sure, let's solve **Exercise 21** step by step.

### Given:
- **Average Speed of the truck**: $$ 70 \, \text{km/h} $$
- **Distance from Johannesburg to Pietermaritzburg**: $$ 420 \, \text{km} $$

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### 1.a) **Calculating the Time Taken for the Journey**

**Formula to use:**
$$
\text{Time} = \frac{\text{Distance}}{\text{Speed}}
$$

**Plugging in the values:**
$$
\text{Time} = \frac{420 \, \text{km}}{70 \, \text{km/h}} = 6 \, \text{hours}
$$

**Answer:**  
The truck will take **6 hours** to travel from Johannesburg to Pietermaritzburg.

---

### 1.b) **Determining the Required Speed to Complete the Journey in 3 Hours**

**Given:**
- **Desired Time**: $$ 3 \, \text{hours} $$
- **Distance**: $$ 420 \, \text{km} $$

**Formula to use:**
$$
\text{Speed} = \frac{\text{Distance}}{\text{Time}}
$$

**Plugging in the values:**
$$
\text{Speed} = \frac{420 \, \text{km}}{3 \, \text{hours}} = 140 \, \text{km/h}
$$

**Answer:**  
To complete the journey in **3 hours**, the truck must travel at an average speed of **140 km/h**.

---

### **Summary:**
- **a)** Time taken at 70 km/h = **6 hours**
- **b)** Required speed for a 3-hour journey = **140 km/h**

If you have any more questions or need further clarification, feel free to ask!
**Exercise 21 Solutions:** 1. **a)** - **Time Taken:** 6 hours 2. **b)** - **Required Speed:** 140 km/h

Execise 21 1) A truck travels at an average speed of \( 70 \mathrm{~km} / \mathrm{h} \). a) If the truck travels a distance of 420 km from Johannesburg to Pietermaritzburg, how long will the jo take? b) What speed would the truck have to travel at to make the journey in 3 hours?

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