 # Radius of Circles From Their Area

In this worksheet, students calculate the radius of a circle given its area. Key stage:  KS 3

Curriculum topic:   Geometry and Measures

Curriculum subtopic:   Solve Problems Involving Perimeters and Areas of 2D Shapes

Difficulty level:   ### QUESTION 1 of 10

The formula for the area of a circle, A, in terms of its radius, r, is:

A = πr2

We can rearrange this formula to make r the subject.

The formula for the radius of a circle, r, in terms of its area, A, is: Example

Calculate the radius, r cm, of a circle which has an area of 100 cm2

r2 = 100 ÷ π = 31.831

r = √31.831 = 5.641896 ≈ 5.64 cm (3 s.f.)

Calculate the radius, r cm, of a circle which has an area of 200 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 400 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 150 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 250 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 650 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 10 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 1 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 1000 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 1250 cm2

(Just write the number)

Calculate the radius, r cm, of a circle which has an area of 201 cm2

(Just write the number)

• Question 1

Calculate the radius, r cm, of a circle which has an area of 200 cm2

(Just write the number)

7.98
EDDIE SAYS
• Question 2

Calculate the radius, r cm, of a circle which has an area of 400 cm2

(Just write the number)

11.3
EDDIE SAYS
• Question 3

Calculate the radius, r cm, of a circle which has an area of 150 cm2

(Just write the number)

6.91
EDDIE SAYS
• Question 4

Calculate the radius, r cm, of a circle which has an area of 250 cm2

(Just write the number)

8.92
EDDIE SAYS
• Question 5

Calculate the radius, r cm, of a circle which has an area of 650 cm2

(Just write the number)

14.4
EDDIE SAYS
• Question 6

Calculate the radius, r cm, of a circle which has an area of 10 cm2

(Just write the number)

1.78
EDDIE SAYS
• Question 7

Calculate the radius, r cm, of a circle which has an area of 1 cm2

(Just write the number)

0.564
EDDIE SAYS
• Question 8

Calculate the radius, r cm, of a circle which has an area of 1000 cm2

(Just write the number)

17.8
EDDIE SAYS
• Question 9

Calculate the radius, r cm, of a circle which has an area of 1250 cm2

(Just write the number)

19.9
EDDIE SAYS
• Question 10

Calculate the radius, r cm, of a circle which has an area of 201 cm2

(Just write the number)

8.00
EDDIE SAYS 