a. Area of the shaded portion = Area of the outer circle – Area of the inner circle
= π R2 – π F= π × 102 – π × 82
= 100π – 64π = 36π
= 36 × 3.14 = 113.04 cm2
b. Outer radius = 7 + 2 = 9 cm Inner radius = 7 cm
Area of the shaded portion = π × 92 - π × 72
= 81π – 49π = 32π = 32 × 3.14 = 100.48 cm2
c. Outer radius = 10.5
Inner radius = 10.5 – 1 = 9.5
Area of the shaded portion = π × (10.5)2 – π × (9.5)2
= π × (10.52 – 9.5)2
= π × (10.52 – 9.52)2
= π × (10.5 + 9.5) (10.5 – 9.5) = π × 20 × 1 = 62.8 cm2
d. Outer radius = \(\frac{16\pi}{2\pi}=8\)
Inner radius = \(\frac{14\pi}{2\pi}=7\)
Area of the shaded portion
