# Circles · Grade 6

> Circles, Grade 6: Centre, radius, diameter and chord, The area of a disc and more. Explanation, worked examples and free practice following the Israeli curriculum.

In Circles (Grade 6) you practise 3 skills: Centre, radius, diameter and chord · The circumference of a circle · The area of a disc.

A circle is a round closed line, and every point on it is the same distance from the centre. The disc is the whole region the circle closes in. A radius is a segment from the centre to the circle. A chord joins two points on the circle, and a diameter is the chord through the centre. The diameter is twice as long as the radius, and it is the longest chord.

Roll a circle one full turn and it travels a little more than three diameters. The exact number is called pi, and it is about 3.14. So the circumference of a circle is about 3.14 times the diameter.

The area of a disc is more than 3 times the radius times the radius, but less than 4 times. It is about 3.14 times the radius times the radius. When the radius is twice as long, the circumference is twice as big, but the area is four times as big. The third level has a challenge, too: the area of a ring between two circles.

**Tip:** When you are given the radius, double it to get the diameter before you work out the circumference.

## What you learn

### Centre, radius, diameter and chord

- Example: (A round shape, shaded all over) What is drawn here, a circle or a disc?
- Options: A disc · A circle
- Answer: A disc
- Solution: The whole region inside the line is shaded, so this is a disc.

### The circumference of a circle

- Example: (A circle with a diameter of length 10) The diameter of the circle is 10 cm. What is its circumference? Use π ≈ 3.14
- Answer: 31.4 cm
- Solution: The circumference of a circle is π times the diameter, about 3.14 times the diameter: 3.14 × 10 = 31.4

### The area of a disc

- Example: (A disc with a radius of length 10) The radius of the disc is 10 cm. What is the area of the disc? Use π ≈ 3.14
- Answer: 314 cm²
- Solution: The area of a disc is π times the radius times the radius: 10 × 10 = 100 Multiply by 3.14: 3.14 × 100 = 314

## Not on the site yet

- Naming a sector and an arc
- Polygons and circles

The exercises are made by rules and the answers are worked out in code. The topic follows the new Israeli elementary programme (2023).

[Practise on the site](https://kixplo.com/il/en/) · [All Grade 6 topics](https://kixplo.com/il/en/math/grade-6/2023/)