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Find Circumferences of Circles Using Their Radii (1)

In this worksheet, students use formulae to calculate the circumferences of circles given their radii.

'Find Circumferences of Circles Using Their Radii (1)' worksheet

Key stage:  KS 3

Curriculum topic:   Geometry and Measures

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

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

This worksheet is about finding the circumferences of circles.

The circumference of a circle is its perimeter or the distance around its edge.

 

You must learn these two important formulae for a circle of radius, r or diameter, d:

 

Circumference of a circle = 2πr

Circumference of a circle = πd

 

 

 

Example 1

Find the circumference of a circle of radius 6 cm.

 

Answer

Circumference = 2 × π × r = 2 × π × 6 = 12 × π = 37.7 cm  (1 decimal place)

 

 

Example 2

Find the circumference of a circle of diameter 6 cm.

 

Answer

Circumference = π × d = π × 6 = 18.8 cm  (1 decimal place)

 

Use a scientific calculator to work out your answer.  If you don't have one in the house, you can access one online.

 

Find the circumference of a circle of radius 25 cm.  

 

Give your answer to 1 decimal place.

 

Use a scientific calculator to work out your answer.  If you don't have one in the house, you can access one online.

Find the circumference of a circle of radius 5 cm.

 

(Just write the number to 1 decimal place)

Find the circumference of a circle of radius 7 cm.

 

(Give your answer to 1 decimal place)

Find the circumference of a circle of radius 10 cm.

 

(Just write the number to 1 decimal place)

Find the circumference of a circle of radius 3.5 cm.

 

(Just write the number to 1 decimal place)

Find the circumference of a circle of diameter 4 cm.

 

(Just write the number to 1 decimal place)

Find the circumference of a circle of diameter 10 cm.

 

(Just write the number to 1 decimal place)

Find the circumference of a circle of diameter 14 cm.

 

(Just write the number to 1 decimal place)

Find the circumference of a circle of diameter 12 cm.

 

(Just write the number to 1 decimal place)

Find the circumference of a circle of diameter 42 cm.

 

(Give your answer to 1 decimal place)

  • Question 1

Find the circumference of a circle of radius 25 cm.  

 

Give your answer to 1 decimal place.

 

Use a scientific calculator to work out your answer.  If you don't have one in the house, you can access one online.

CORRECT ANSWER
EDDIE SAYS
How did you get on with the first question? Did you remember to use the formula? Once you've learned this, you'll be able to do these standing on your head... it's all about the practice! Then, we just substitute the number (replace) them in the formula and work out the calculation. 2 × π × 25
  • Question 2

Find the circumference of a circle of radius 5 cm.

 

(Just write the number to 1 decimal place)

CORRECT ANSWER
EDDIE SAYS
How did you do here? Did you, first of all, remember the formula before substituting the numbers in? 2 × π × 5 It really is just a case of committing this to memory!
  • Question 3

Find the circumference of a circle of radius 7 cm.

 

(Give your answer to 1 decimal place)

CORRECT ANSWER
EDDIE SAYS
Are you getting in the swing of things now? You needed to calculate 2 × π × 7 = 44 or 44.0
  • Question 4

Find the circumference of a circle of radius 10 cm.

 

(Just write the number to 1 decimal place)

CORRECT ANSWER
EDDIE SAYS
It's really important that you read the question carefully. It has asked you to write this answer to one decimal place. if you didn't, you could have been marked wrong for this question, just like you would be in a test. Let's get into good habits early! 2 × π × 10
  • Question 5

Find the circumference of a circle of radius 3.5 cm.

 

(Just write the number to 1 decimal place)

CORRECT ANSWER
EDDIE SAYS
Are you feeling pretty confident with this now? Remember to read the instructions carefully first each time and don't just assume that you know what it's asking! 2 × π × 3.5
  • Question 6

Find the circumference of a circle of diameter 4 cm.

 

(Just write the number to 1 decimal place)

CORRECT ANSWER
12.6
EDDIE SAYS
Did you read this question carefully? If you did you would have seen that this time you are given the diameter and not the radius. So, this time we need to use this formula π d So, the calculation we need to complete is: π x 4
  • Question 7

Find the circumference of a circle of diameter 10 cm.

 

(Just write the number to 1 decimal place)

CORRECT ANSWER
EDDIE SAYS
Did you read this carefully again? We can use π x d for this one too, and when we substitute we get: π × 10
  • Question 8

Find the circumference of a circle of diameter 14 cm.

 

(Just write the number to 1 decimal place)

CORRECT ANSWER
EDDIE SAYS
Are you getting the hang of this? Hopefully, you are feeling more confident with these calculations. Just substitute the numbers into the formula. π × 14
  • Question 9

Find the circumference of a circle of diameter 12 cm.

 

(Just write the number to 1 decimal place)

CORRECT ANSWER
EDDIE SAYS
You'll be doing this in your sleep soon! π × 12 How are you getting on? Last queston coming up!
  • Question 10

Find the circumference of a circle of diameter 42 cm.

 

(Give your answer to 1 decimal place)

CORRECT ANSWER
EDDIE SAYS
You needed to calculate π × 42 = 131.9468 When we round this to one decimal place we get 131.9. Great work, that's another activity completed!
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