Ratio: A ratio shows the relative sizes of two or more values.

Equal parts: all parts in the same proportion, or a whole shared equally

Proportion: A statement that lines two ratios

Equivalent: Having the same value

Gradient: How steep a line is.

Diameter: The distance from one point on a circle through the centre to another point on the circle. Diameter is twice the radius.

Circumference: The distance around the edge of a circle. It is a type of perimeter.

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Command words:   

Express means to write. 

Express in ratio notation: A ratio is written with a colon between the two quantities that are being compared. (e.g. A to B =  3 : 5) 

Simplify the ratio: Write the ratio in its simplest form. (The numbers have no common factors other than 1.)