Correct Answer - Option 3 : 1,320 cm
2
Given:
Inner diameter of hollow cylindrical pipe = 8 cm
Outer diameter = 12 cm
Height of cylinder (h) = 21 cm
Concepts used:
CSA of hollow cylinder = 2π × (r + R) × h
Calculation:
Inner radius (r) of cylindrical pipe = ½ × Inner diameter of cylinder = 8/2 cm = 4 cm
Outer radius (R) of cylinder = ½ × Outer diameter of cylinder = 12/2 cm = 6 cm
CSA of hollow cylindrical pipe = 2 × 22/7 × (4 + 6) × 21 cm2
⇒ CSA = 1,320 cm2
∴ CSA of hollow cylindrical pipe is equal to 1,320 cm2.