Question

A rectangular sheet of paper $40cm\times 22cm,$ is rolled to form a hollow cylinder of height 40 cm. The radius of the cylinder (in cm) is

(a) 3.5 (b) 7 (c) $\frac{80}{7}$ (d) 5

Answer 1

Given,

A rectangular sheet of paper $=40cm\times 22cm$ is rolled to form a hollow sphere height of 40 cm.
when the sheet is rolled 22 cm becomes the circumference of the base circles.
circumference = 22 cm

$\Rightarrow 2\pi r=22cm$
$\Rightarrow 2\times \frac{22}{7}\times r=22cm$
$\Rightarrow r=22\times \frac{1}{2}\times \frac{7}{22}$

$\Rightarrow r=\frac{7}{2}$
$\Rightarrow r=3.5$
Now we got the radius as 3.5 cm