Question

Find the surface area of a frustum of cone, whose larger and smaller radius is 1.5 cm and 0.2 cm. The slant height of the cone is 2.5 cm. (Use $\pi$ = 3.14)

• A. 20.666 cm${}^2$
• B. 21.666 cm${}^2$
• C. 22.666 cm${}^2$
• D. 23.666 cm${}^2$

Answer 1

The correct option is B 21.666 cm${}^2$

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

R = 1.5 cm, r = 0.2 cm, s = 2.5 cm

SA = $\pi$(0.2 + 1.5)2.5 +$\pi$0.2${}^2$ + $\pi$1.5${}^2$

= $\pi$(1.7)2.5 + 0.4$\pi$ + 2.25$\pi$

= 3.14 $\times$ (4.25 + 0.4 + 2.25)

= 3.14 $\times$ 6.9

= 21.666 cm${}^2$