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Radius of Circles From Their Area

In this worksheet, students calculate the radius of a circle given its area.

'Radius of Circles From Their Area' worksheet

Key stage:  KS 3

Curriculum topic:  Geometry and Measures

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

Difficulty level:  

down

Worksheet Overview

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

Give your answer to 3 sig. figs.

 

Answer

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

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

Give your answer to 3 sig. figs.

(Just write the number)

  • Question 1

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
7.98
EDDIE SAYS
Radius = √(200 ÷ π)
  • Question 2

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
11.3
EDDIE SAYS
Radius = √(400 ÷ π)
  • Question 3

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
6.91
EDDIE SAYS
Radius = √(150 ÷ π)
  • Question 4

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
8.92
EDDIE SAYS
Radius = √(250 ÷ π)
  • Question 5

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
14.4
EDDIE SAYS
Radius = √(650 ÷ π)
  • Question 6

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
1.78
EDDIE SAYS
Radius = √(10 ÷ π)
  • Question 7

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
0.564
EDDIE SAYS
Radius = √(1 ÷ π)
  • Question 8

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
17.8
EDDIE SAYS
Radius = √(1000 ÷ π)
  • Question 9

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
19.9
EDDIE SAYS
Radius = √(1250 ÷ π)
  • Question 10

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

Give your answer to 3 sig. figs.

(Just write the number)

CORRECT ANSWER
8.00
EDDIE SAYS
Radius = √(201 ÷ π)
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