2020 · Q74
The thickness of a cylinder is 1 foot, the inner radius of the cylinder is 3 feet and height is 7 feet. To paint the inner surface it requires one litre of a particular colour. How much quantity of the same colour is required to paint all the surfaces of the cylinder?
Elementary MathematicsMensuration
- A7/3 litre
- B3/2 litre
- C8/3 litre
- D10/3 litre
Explanation
Inner curved area = 2π × 3 × 7 = 42π sq ft needs 1 litre. All surfaces = outer curved 56π + inner curved 42π + two annular ends 2 × 7π = 112π sq ft. Paint needed = 112π/42π = 8/3 litres.