Question

Calculate the total surface area of a frustum of cone whose upper base radius is 4 cm and lower base radius is 1 cm and its height is 4 cm. (Use $\pi$ = 3).

• A. 126 cm${}^2$
• B. 116 cm${}^2$
• C. 136 cm${}^2$
• D. 226 cm${}^2$

Answer 1

Answer: (A)

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

R = 4 cm, r = 1 cm, h = 4 cm

$=3\times (1+4)\sqrt{(4-1{)}^2+4^2}+3\times 1^2+3\times 4^2$

$=3\times \left(5\right)\sqrt{(3{)}^2+4^2}+3+3\times 16$

$=15\sqrt{9+16}+3+48$

$=15\times \sqrt{25}+51$

$=15\times 5+51$

$=126c{m}^2$