Question

Direction: A hollow cylindrical tank whose bottom is closed and top is open is painted from outside as well as inside. The inner radius of the cylinder is $7cm$, and its thickness is $2cm$. The height of the cylinder is $21cm$.

Find the approximate area (in $sqcm$) of the painted surface.

• A. $2256$
• B. $2467$
• C. $3214$
• D. $1983$

Answer 1

The correct option is B $2467$

The required area = Outer curved surface area + Inner curved surface area + Area of the base + Area of the open top

$=2\pi \times 9\times 21+2\pi \times 7\times 21+\pi (9{)}^2+\pi (9^2-7^2)$
$=2\times \frac{22}{7}\times 9\times 21+2\times \frac{22}{7}\times 7\times 21+\frac{22}{7}\times 81+\frac{22}{7}\times 26\times 2$
$=1188+927+\frac{22}{7}\times 113=2112+355.14\approx 2467Sqcm$
Hence, option $C$ is the correct answer.