Calculate, correct to 3 significant figures, the circumference of a circle with:

(A) radius 7 cm

(B) radius 10 cm

(C) radius 12 cm.                                                                                                                                                                                  [Page No. 129]

Formula: $C = 2\pi r$

(A) $r = 7 \text{ cm}$:

$$C = 2 \times \frac{22}{7} \times 7$$

$$= 2 \times 22 = 44.0 \text{ cm}$$

(B) $r = 10 \text{ cm}$:

$C = 2 \times \frac{22}{7} \times 10 = \frac{440}{7} \approx 62.857\dots \approx 62.9$ cm

(C) $r = 12 \text{ cm}$:

$C = 2 \times \frac{22}{7} \times 12 = \frac{528}{7} \approx 75.428... \approx 75.4$ cm