Question

Find the curved surface area of a frustum of a cone. The slant height is $15\text{cm}$, top and bottom diameter is $4\text{cm}$ and $10\text{cm}$ respectively. (Use $\pi =3$)

• A. $1,260{\text{cm}}^2$
• B. $1,265{\text{cm}}^2$
• C. $1,660{\text{cm}}^2$
• D. $1,560{\text{cm}}^2$

Answer 1

The correct option is A $1,260{\text{cm}}^2$

Curved surface area of a frustum of cone is given by $\pi l(R+r).$

Given $\Rightarrow$ $R=20\text{cm},r=8\text{cm}$

So,

$\begin{array}{cc}A& =3\times 15(20+8)\\ & =45\left(28\right)\\ & =1260{\text{cm}}^2\end{array}$

Hence, the curved surface area of the frustum of the cone is equal to $1260{\text{cm}}^2.$