Selina Concise Class 9 Maths Chapter 20 Area and Perimeter Of A Plane Figures Exercise 20C Solutions
EXERCISE – 20C
(1) The diameter of a circle is 28 cm.
Find it’s (i) Circumference
(ii) Area
Solution:
Given:
Diameter = 28cm.
∴ radius = diameter/2
= 28/2
(r) radius = 14 Cm.
(i) Circumference = 2 π r.
= 2 × 22/7 × 14
= 2 × 22 × 2
= 88
(ii) Area of Circle = π r2
= 22/7 × (14)2
= 22/7 × 14 × 14
= 22 × 14 × 2
= 44 × 14
= 616 Cm2.
(2) The Circumference of a Circular field is 308 m. Find is:
(i) Radius
(ii) Area.
Solution:
Given: Circumference = 308 m
2 π r = 308
r = 308/2 π
r = 308/2 × 22/7
r = 154 × 7/ 22
r = 7 × 7
r = 49 m
Area of circle = πr2
= 22/7 × (49)2
= 22/7 × 49 × 49
Area of circle = 22 × 49 × 7
= 7. 546 cm2
(3) The Sum of the circumference and diameter of a circle is 116 cm. Find it’s radius.
Solution:
Given:
The Sum of the circumference and diameter of a circle is 116 cm.
C + d = 116 cm
2 π r + 2r = 116
2r (π + 1) = 116
r (π + 1) = 116/2
r (π + 1) = 58
r = 58/ π + 1
r = 58/22/7 + 1
r = 58/22/7 + 7
r = 58 × 7/ 29
r = 2 × 7
r = 14 cm
(4) The radii of two circles are 25 cm and 18 cm. Find the radius of the circle which has circumference equal to the sum of circumferences of these two circles.
Solution:
Let r1 = 25 cm
R2 = 18 cm
Circumference = C1 + C2
2 π r = 2 π r1 + 2 π r2
2 π r = 2 π ( r1 + r2)
2 π r = r1 + r2
r = r1 + r2
r = 25 + 18
r = 43 cm
∴ The radius of the circle is 43 cm.
(5) The radii of two circle 48 cm and 13 cm find the area of the circle which has it’s circumference equal to the difference of the circumferences of the given two circles.
Solution:
Circumference = C1 – C2
The Circumference equal to the difference of the circumferences of the given two circles.
∴ circumference = C1 – C2
2 π r = 2 π r1 – 2 π r2
2 π r = 2 π ( r1 – r2)
r = r1 – r2
r = 48 – 13
r = 35 cm
Area of circle = πr2
= 22/7 × (35)2
= 22/7 × 35 × 35
= 22 × 35 × 5
= 110 × 35
= 3850 cm2
∴ The area of circle is 3850 Cm2.
Here is your solution of Selina Concise Class 9 Maths Chapter 20 Area and Perimeter Of A Plane Figures Exercise 20C
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