Question

The surface area of a frustum cone is 11,000 cm2. The larger and smaller radius of the cone is 10 and 5 cm. find its slant height. (Use $\pi$ = 22/7)

• A. 215 cm
• B. 235 cm
• C. 245 cm
• D. 225 cm

Answer 1

Answer: (D)

225 cm

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

R = 10cm, r = 5cm, SA = 11,000 cm2

11,000 $=$ 22/7 $\times$ (5 +10)s +$\pi$5${}^2$ + $\pi$10${}^2$

11,000 $=$ 22/7 $\times$ [15s +25 + 100]

11,000 $=$ 22/7 $\times$ [15s +125]

11,000 $\times$ 7/22$=$ 15s + 125

3,500 125$=$ 15s

3,375/15 $=$ s

S $=$ 225 cm

Therefore, the slant height is 225 cm.