# Circles - Using π - Level 4

## Practise using pi to calculate various circle measurements.

##### Level 1Level 2Level 3Level 4Level 5Level 6Exam-StyleDescriptionHelp

This is level 4; the areas of circles are given, find either the radius, diameter or circumference. Give your answers correct to three significant figures. You can earn a trophy if you get at least 7 correct. The diagrams are not drawn to scale.

 AREA   Calculate the radius of a circle if the area is 74.6cm2. cm Calculate the radius of a circle if the area is 75.7cm2. cm Calculate the diameter of a circle if the area is 83.5cm2. cm Calculate the diameter of a circle if the area is 86.8cm2. cm Calculate the circumference of a circle if the area is 94cm2. cm Calculate the circumference of a circle if the area is 102.3cm2. cm A circle is drawn inside a square so its circumference touches each of the four sides of the square. If the area of the circle is 109.4cm2 calculate the length of the sides of the square. cm A different circle is drawn inside a square so its circumference touches each of the four sides of the square. If the area of the circle is 116.8cm2 calculate the area of the square. cm2 Two circles are drawn inside a rectangle so their circumferences touch each other and three sides of the rectangle. If the areas of the circles are 6.9cm2 each, calculate the area of the rectangle. cm The area of the large circle is 12.7cm2 and area of the small circle is 5.2cm2. How many times larger is the radius of the large circle than the radius of the small circle?
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This is Circles - Using pi level 4. You can also try:
Level 1 Level 2 Level 3 Level 5 Level 6 Composites

## Instructions

Try your best to answer the questions above. Type your answers into the boxes provided leaving no spaces. As you work through the exercise regularly click the "check" button. If you have any wrong answers, do your best to do corrections but if there is anything you don't understand, please ask your teacher for help.

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## Description of Levels

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Level 1 - find the circumference given the radius or diameter.

Level 2 - find the radius or diameter given the circumference.

Level 3 - find the area of a circle given either the radius or diameter.

Level 4 - the areas of circles are given, find either the radius, diameter or circumference.

Level 5 - the radius and angle subtended at the centre of the circle are given, find the length of the arc or area of the sector of the circle.

Level 6 - this level has mixed questions about the circle. Most of these questions will require a multi-part calculation once the situation described in the question has been understood.

Areas of composite shapes requires an ability to calculate the areas of other shapes such as rectangles, triangles and trapezia.

Exam Style questions are in the style of GCSE or IB/A-level exam paper questions and worked solutions are available for Transum subscribers.

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## Help with circle calculations

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Use a calculator for this exercise. All of the calculations you will do involve the number π (pronounced pi) which is roughly equal to 3.141592. You should use the π button on your calculator to get this number into your calculation.

Let r be the radius, d the diameter, C the circumference and A the area of a circle.

C = πd    [i.e., to find the circumference multiply the length of the diameter by pi]

A = πr2    [i.e., to find the area multiply the square of the radius by pi]

For arcs multiply the circumference by the angle subtended at the centre and divide by 360.

For sector area multiply the circle area by the angle subtended at the centre and divide by 360.

For help using a calculator with circle calculations see Calculator Workout.

For more on this topic see our Circles page.

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