Question

The surface area of a frustum cone is 330 in2. The larger and smaller radius of the cone is 2.2 and 1in. Find its slant height. (Use $\pi$ = 3.14)

• A. 2.6 in
• B. 3.6 in
• C. 5.6 in
• D. 4.6 in

Answer 1

The correct option is C 5.6 in

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

R = 2.2in, r = 1 in, SA = 330 in2

330 $=$ 3.14 $\times$ (1 + 2.2)s +$\pi$1${}^2$ + $\pi$2.2${}^2$

330 $=$ 3.14 $\times$ [3.2s +1 + 4.84]

330 $=$ 3.14 $\times$ [3.2s + 5.84]

330/3.14 $=$ 3.2s + 5.84

105.09/5.84 $=$ 3.2s

17.994/3.2 $=$ s

S $=$ 5.6 in

Therefore, the slant height is 5.6 in.