Question

Find the surface area of a frustum of cone given below:

• A. 122.25$\pi$ cm${}^2$
• B. 112.25$\pi$ cm${}^2$
• C. 132.25$\pi$ cm${}^2$
• D. 142.25$\pi$ cm${}^2$

Answer 1

The correct option is B 112.25$\pi$ cm${}^2$

Surface area of a frustum of cone $=\pi (r+R)s+\pi r^2+\pi R^2$

R = 2.5 cm, r = 1 cm, s = 30 cm

$=\pi (1+2.5)30+\pi 1^2+\pi {2.5}^2$

$=105\pi +\pi +6.25\pi$

$=112.25=\pi (1+2.5)30+\pi 1^2+\pi {2.5}^2$

$=105\pi +\pi +6.25\pi$

$=112.25\pi c{m}^2$