Question

In a building there are 4 cylindrical pillars. The radius of each pillar is 21 cm and height is 5 m. Find the curved surface area of four pillars.

Answer 1

Hint: The curved surface area is the area in which we just cover the side view not top and bottom views. So we can use direct formula of curved surface area of cylinder i.e. $2\pi rh$
Where, $r$ is the radius of a cylindrical pillar and $h$ Is the height of a cylindrical pillar.
$\pi = \dfrac{{22}}{7}$ Or $3.14$.

Complete step by step answer:
Given,
The radius of the pillar $ = 21cm$
The height of pillar $ = 5m = 500cm$
Now, curved surface area of one cylindrical pillar is $ = 2\pi rh$
                                                                                            $ = 2 \times \dfrac{{22}}{7} \times 21 \times 500$
                                                                                            $ = $$6 \times 22 \times 500$
                                                                                             $ = 66000c{m^2}$
$\therefore $ Curved surface area of $4$ pillars $ = $$4 \times $curved surface area of one pillar
                                                               $ = 4 \times 66000$
                                                               $ = 264000c{m^2}$ Or $26.4{m^2}$
Which is the required answer.
Additional information: The total and curved surface areas are found generally for the 3D figures. In this question we are finding the curved surface area which means area of the side view only not considering the area of the top and the bottom view.

Note: Generally mistakes can be made during conversion of $m$ into $cm$ or vice versa. One can also make mistakes by using the formula of surface area instead of using curved surface area. They both are different, so be careful when solving questions.