Question

There is a hollow cylinder as shown in the figure having outer radius 7 cm, height 21 cm and inner radius 6 cm, whose inner and outer surfaces are to be painted. Calculate the area to be painted.

• A. $792c{m}^2$
  
• B. $924c{m}^2$
  
• C. $1716c{m}^2$
  
  
• D. $132c{m}^2$

Answer 1

The correct option is C

$1716c{m}^2$

Area to be painted = inner curved surface area + outer curved surface area
Let inner radius be $r_1$ and outer radius be $r_2$ .
Required area = Curved surface area of the hollow cylinder = $2\pi r_{1}h+2\pi r_{2}h$
$Area=2\pi h(r_1+r_2)$
$Area=2\times \frac{22}{7}\times 21(7+6)$
= $1716c{m}^2$