Let's solve the problems one by one based on the image provided:

Section 1:

Given: $\pi = 3.14$ and round answers to 1 decimal place (1 d.p.).

• (a) $d = 4 \, \text{cm}$
  Formula: $C = \pi d$
  Calculation: $C = 3.14 \times 4 = 12.56 \, \text{cm}$
  Rounded: $C = 12.6 \, \text{cm}$

• (b) $d = 5 \, \text{cm}$
  Formula: $C = \pi d$
  Calculation: $C = 3.14 \times 5 = 15.7 \, \text{cm}$
  Rounded: $C = 15.7 \, \text{cm}$

Section 2:

Given: $\pi = 3.142$ and round answers to 2 decimal places (2 d.p.).

• (a) $d = 8 \, \text{cm}$
  Formula: $C = \pi d$
  Calculation: $C = 3.142 \times 8 = 25.136 \, \text{cm}$
  Rounded: $C = 25.14 \, \text{cm}$

• (b) $d = 6 \, \text{cm}$
  Formula: $C = \pi d$
  Calculation: $C = 3.142 \times 6 = 18.852 \, \text{cm}$
  Rounded: $C = 18.85 \, \text{cm}$

Section 3:

Use the $\pi$ button on the calculator for more accurate values. Round answers to 2 decimal places (2 d.p.).

• (a) $d = 9 \, \text{cm}$
  Formula: $C = \pi d$
  Calculation: $C \approx 3.14159 \times 9 = 28.27431 \, \text{cm}$
  Rounded: $C = 28.27 \, \text{cm}$

• (b) $d = 12 \, \text{cm}$
  Formula: $C = \pi d$
  Calculation: $C \approx 3.14159 \times 12 = 37.6991 \, \text{cm}$
  Rounded: $C = 37.70 \, \text{cm}$

Would you like more details or have any questions about these calculations?

Here are 5 related questions to deepen your understanding:

1. How is the circumference of a circle related to its diameter?
2. How would the circumference change if the diameter is doubled?
3. What is the difference between using $\pi = 3.14$ and using the $\pi$ button on a calculator?
4. Can you find the radius of the circle if you are given the circumference?
5. What would the circumference be if the diameter were 10 cm, using $\pi \approx 3.14159$?

Tip:

Always check whether you need to round your answers to a specific decimal place to avoid losing marks in exams!