Question

Find the surface area of a frustum of cone, whose larger and smaller radius is 50 m and 20 m. The slant height of the cone is 100 m. (Use $\pi$ = 3)

• A. 29,700 m${}^2$
• B. 28,700 m${}^2$
• C. 27,700 m${}^2$
• D. 26,700 m${}^2$

Answer 1

The correct option is A 29,700 m${}^2$

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

R = 50 m, r = 20 m, s = 100 m

SA = $\pi$(20 + 50)100 +$\pi$20${}^2$ + $\pi$50${}^2$

= $\pi$(70)100 + 400$\pi$ + 2500$\pi$

= 3$\times$ (7000 + 400 + 2500)

= 3 $\times$ 9,900

= 29,700 m${}^2$