Question

Find the circumference of circles whose radii are

(1) 21 cm

(2) 56 cm

(3) 4.2 cm

(4) 10.5 cm

Answer 1

(1) C = 2πr

= 2 × × 21

= 2 × 22 × 3

= 132 cm

(2) C = 2πr

= 2 × × 56

= 2 × 22 × 8

= 352 cm

(3) C = 2πr

= 2 × × 4.2

= 2 × 22 × 0.6

= 26.4 cm

(4) C = 2πr

= 2 × × 10.5

= 2 × 22 × 1.5

= 66 cm