Question

Shaded area is 51 pi cm squared. The diameter of the larger circle is 20cm. Find r

Answer 1

Answer:

R = 4 cm

Step-by-step explanation:

A = pi * r^2

51 = 3.14 r^2

r^2 = 51/3.14

r^2 = 16

r = 4 cm

*Note:- neglect the diameter of the the larger circle

Answer 2

Answer: r = 7

Step-by-step explanation:

The formula for determining the area of a circle is expressed as

Area = πr²

Where

π is a constant whose value is 3.14

r represents the radius of the circle.

From the information given

Diameter of the big circle = 20 cm

Radius = diameter/2

Radius = 20/2 = 10

Area of big circle = π × 10² = 100π

Radius of small circle = r

Area of small circle = πr²

Area of big circle - area of small circle = shaded area

Therefore

100π - πr² = 51π

π(100 - r²)/= 51π

Dividing through by π, it becomes

100 - r² = 51

r² = 100 - 51 = 49

r = √49 = 7