Question

Calculate the total surface area of a frustum of cone whose upper base radius is 15 m and lower base radius is 5 m and its height is 15 m. (Use $\pi$ = 3).

• A. 1,931.66 m${}^2$
• B. 1,831.66 m${}^2$
• C. 1,731.66 m${}^2$
• D. 1,631.66 m${}^2$

Answer 1

Answer: (B)

1,831.66 m${}^2$
Total surface area, SA = (r + R)$\sqrt{(R-r{)}^2+h^2}+\pi r^2+\pi R^2$

R = 15m, r = 5m, h = 15m

$=3\times (5+15)\sqrt{(15-5{)}^2+{15}^2}+3\times 5+3\times {15}^2$

$=3\times \left(20\right)\sqrt{(10{)}^2+{15}^2}+3\times 25+3\times 225$

$=60\sqrt{100+225}+75+675$

$=60\times \sqrt{325}+750$

$=1,831.66m^2$