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# What is a ratio?

A ratio is a relationship between two or more quantities. It expresses the relative proportions of various quantities. A ratio is written with a colon ($:$), as in $3:4$.

A café makes biscuits using $\Tblue{2}$ kilos of flour and $\Tred{1}$ kilo of sugar. The ratio of flour to sugar is $\Tblue{2}:\Tred{1}$.

I make biscuits with $\Tblue{8}$ ounces of flour and $\Tred{4}$ ounces of sugar. The ratio flour to sugar is the same $\Tblue{8}:\Tred{4} = \Tblue{2}:\Tred{1}$, because I need twice as much flour as I need sugar.

Ratios can compare more than two quantities.

My recipe uses as much butter as it does sugar and twice as much flour. The ratio of flour to sugar to butter is $\Tblue{2}:\Tred{1}:\Tviolet{1}$.

Recipes use ingredients in particular ratios.