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Definition: ratio from Philip's Encyclopedia

Number relating two numbers or two quantities of the same kind, such as two prices or two lengths, that indicates their relative magnitude. Ratios, as of the numbers 3 and 4, can be written as a fraction 3/4, or with a colon (3:4).

Summary Article: ratio from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

Measure of the relative size of two quantities or of two measurements (in similar units), expressed as a proportion. For example, the ratio of vowels to consonants in the alphabet is 5:21. As a fraction5/26 of the letters are vowels. The ratio of 500 m to 2 km is 500:2,000, or in its simplest integer form 1:4 (dividing both sides of the ratio by 500).

Ratios are normally expressed as whole numbers, so 2:3.5 would become 4:7 (the ratio remains the same provided both parts of the ratio are multiplied or divided by the same number).

For example, to make up 1 litre of mauve paint, blue, red, and white paints have to be mixed in the ratio 5:2:3. The amount of each colour needed can be worked out as follows:

1 litre is the same as 1,000 ml. The ratio 5:2:3 means 5 parts blue, 2 parts red, and 3 parts white – making 10 parts altogether. 1,000 ÷ 10 = 100, so 1 part = 100 ml. The amounts needed, therefore, are

5 × 100 = 500 ml of blue paint; 2 × 100 = 200 ml of red paint; 3 × 100 = 300 ml of white paint

Alternatively, by dividing the given quantity into the ratio, the quantity for each paint can be found. For instance, the amount of blue paint = 5/10 × 1,000 = 500 ml.


Working out fractions, percentages and ratios

Gimme Five! – Polygons, Ratio, and the use of Trigonometry

Calculating ratios

Ratio calculation

Making a model: using scale factor and enlargement

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