Question

Suppose that there is a conical strainer as shown in the given figure.The radius of its broadest end is 6 cm and length is 8 cm. Now if 2 ${cm}^2$ of strainer has an average of 8 tiny holes, then find the total number of holes in the entire strainer.

• A. 663
• B. 753
• C. 843
• D. 723

Answer 1

The correct option is B

753

Since holes are in the curved surface area of cone so first we have to find the curved surface area of the strainer.

Slant height = $\sqrt{\left(h^2\right)+\left(r^2\right)}$

= $\sqrt{\left(6^2\right)+\left(8^2\right)}$ = 10cm

Now curved surface area of the cone = $\pi$rl

= $\pi$ $\times$ 6 $\times$ 10 = 60 $\pi$ ${cm}^2$

Since 2 ${cm}^2$ srea of strainer has 8 holes

Hence the tonal number of holes in the entire strainer = 60 $\times$ $\pi$ $\times$ $\frac{8}{2}$ = 240 $\times$ $\frac{22}{7}$ = 753.6 or 753 approx.