Question

A rectangular piece of paper of dimensions 20 cm x 14 cm is rolled along the breadth to form a cylinder.
Find the radius of the base of the cylinder so formed.

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Answer 1

$\bf The \: circumference \: of \: the \: base \: is \: 20 \: cm \: we \: know, \\ \bf\: The \: circumference \: of \: the \: cylinder = 2 \times \frac{22}{7} \times r \\ \bf \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: 20= \frac{44}{7} \times r \\ \bf \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: 20× \frac{7}{44} = r \\ \bf \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \huge \boxed {3.18 = r} \\ \bf hence, \: Radius \: of \: the \: cylinder \: is \: 3.18cm$

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Answer 2

given,

length of rectangle = 20 cm

breath of rectangle = 14 cm

to find,

1.radius of cylinder

according to diagram

circumference of circle = 14 cm

so,

2πr = 14 cm

2×22÷7 × r = 14

44÷7 × r= 14

6.28 × r = 14

r= 2.22 cm