Question

The surface area of the frustum cone is $450m^2$ whose top circle radius is $3$ m and bottom circle radius is $2$ m. Find its slant height. (Use $\pi$ = 3)

• A. $27.4$ m
• B. $26.4$ m
• C. $25.4$ m
• D. $24.4$ m

Answer 1

The correct option is A $27.4$ m

Surface area of frustum cone = $\pi (r+R)s+\pi r^2+\pi R^2$
$450=\pi (2+3)s+\pi 2^2+\pi 3^2$
$450=3\times 5s+3\times 4+3\times 9$
$450=15s+12+27$
$450=15s+39$
$450-39=15s$
$411÷15=s$
Slant height, $s=27.4$ m