Question

The outer diameter of a gas cylinder is 20 centimeters. Find the cost of painting of its outer curved surface at ₹4 per square centimeter if the height of the cylinder is 70 centimeter.

Answer 1

Outer radius, r = 20/2 = 10 cm
Height, h = 70 cm
$curved \: surface \: area = 2\pi \: rh \\ = 2 \times \frac{22}{7} \times 10 \times 70 = 4400 \: {cm}^{2} \\ \\ cost \: of \: painting = 4400 \times 4 \\ = Rs. \: 17600$

Answer 2

as you know

the lateral (or curved) surface area of a cylinder = 2πrh

=2π10* 70

=1400*22/7

=4400*4

=17600

thus, the cost of painting its outer curved surface at Rs. 4 is rs.17600