Ratio
A comparison between two quantities (multitudes or magnitudes) of the same type, where we compare them in terms of their relative size.
For example:
- A count of apples to a count of oranges, since both are multitudes (a “count”).
- A distance of one mile to a distance of five miles, since both are magnitudes (“distance”) of the same type.
The things being compared are called the “terms” of the ratio.
Ratios are written in the form “𝑎 : 𝑏 ” for the two quantities (“terms”) being compared.
The first term, 𝑎, is called the antecedent term, and the second term, 𝑏, is called the consequent term.
The convention for writing ratios uses:
- whole numbers, so “3 : 2” rather than “1.5 : 1”
- lowest terms, so “2 : 1” rather than “4 : 2”.
Related terms: rational number, irrational number
Why Ratios Matter
A ratio is a comparison that takes place in the mind.
But they describe very real relationships between things in the world.
The ratio of your income to your expenses, is the difference between saving money or being driven into debt.
The ratio of deaths from a disease to people infected (with the disease), tells you how deadly the disease is.
