 # RS Aggarwal Solutions for Class 6 Chapter 21 Concept of Perimeter and Area Exercise 21B

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1. Find the circumference of a circle whose radius is

(i) 28 cm

(ii) 10.5 cm

(iii) 3.5 m

Solutions

(i) Given radius = 28 cm

We know that

Circumference of the circle i.e C = 2πr

= (2 × 22 / 7 × 28) {π = 22 / 7}

= (56 × 22 / 7)

= 176 cm

Thus, the circumference of the circle is 176 cm

(ii) Given radius = 10.5 cm

We know that

Circumference of the circle, C = 2πr

= (2 × 22 / 7 × 10.5) {π = 22 / 7}

= (21 × 22 / 7)

= 66 cm

Thus, the circumference of the circle is 66 cm

(iii) Given radius = 3.5 m

We know that

Circumference of the circle, C = 2πr

= (2 × 22 / 7 × 3.5)

= (7 × 22 / 7)

= 22 m

Thus, the circumference of the circle is 22 m

2. Find the circumference of a circle whose diameter is

(i) 14 cm

(ii) 35 cm

(iii) 10.5 m

Solutions

(i) Given

Diameter = 14 cm

Circumference of the circle, C = 2πr

= π × (2r)

= π × diameter of the circle {diameter = 2r}

= 22 / 7 × 14

= 44 cm

Hence, the circumference of the circle is 44 cm

(ii) Given

Diameter = 35 cm

Circumference of the circle, C = 2πr

= π × (2r)

= π × diameter of the circle {diameter = 2r}

= 22 / 7 × 35

= 110 cm

Hence, the circumference of the circle is 110 cm

(iii) Given

Diameter = 10.5 m

Circumference of the circle, C = 2πr

= π × (2r)

= π × diameter of the circle {diameter = 2r}

= 22 / 7 × 10.5

= 33 m

Hence, the circumference of the circle is 33 m

3. Find the radius of a circle whose circumference is 176 cm.

Solution

Given

Circumference of the circle = 176 cm

Let r cm be the radius of the given circle

Circumference of the circle = 2πr

2πr = 176

r = 176 / 2π

r = (176 / 2) × (7 / 22) {π = 22 / 7}

r = 88 × 0.31

r = 27.28

r = 28 cm

Hence, the radius of the circle is 28 cm

### Access other exercises of RS Aggarwal Solutions for Class 6 Chapter 21 Concept of Perimeter and Area

Exercise 21E Solutions