Ex.11.3 Q2 Perimeter and Area - NCERT Maths Class 7

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Question

Find the area of the following circles, given that:\begin{align}\left( {{\rm{Take\, }}\pi = \frac{{22}}{7}} \right)\end{align}

(a) Radius $$= 14\,\rm mm$$

(b) Diameter $$= 49 \,\rm m$$

(c) Radius $$= 5 \,\rm cm$$

Video Solution
Perimeter And Area
Ex 11.3 | Question 2

Text Solution

What is known?

Radius or diameter of the circles.

What is unknown?

The Area of the circles.

Reasoning:

In this question, radius (or diameter) of the circle is given. Put the value of the radius in the formula of area of the circle to find out the area.

Steps:

(a) Given,

Radius of the circle $$= 14 \,\rm mm$$

Area of circle

\begin{align}&= \pi {r^2}\\&= \frac{{22}}{7} \times 14 \times 14\\&= 22 \times 2 \times 14\\&= 616\;\rm m{m^2}\end{align}

(b) Given,

Diameter of the circle $$= 49 \,\rm m$$

Therefore, radius $$= 24.5 \,\rm m$$

Area of circle

\begin{align}&= \pi {r^2}\\&= \frac{{22}}{7} \times 24.5 \times 24.5\\&= 22 \times 24.5 \times 3.5\\&= 1886.5\;\rm {m^2}\end{align}

(c) Given,

Radius of the circle $$= 5 \,\rm cm$$

Area of circle

\begin{align}&= \pi {r^2}\\&= \frac{{22}}{7} \times 5 \times 5\\ &= \frac{{550}}{7}\\&= 78.57\;\rm c{m^2}\end{align}

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