A rate of $10 per hour


A rate is a comparison between two quantities of a different type (rather than of the same type).

The things being compared are called the “terms” of the rate.

For example:

Rates can be written in the standard ratio form of “𝑎 : 𝑏 ”, for the two quantities (“terms”) being compared, but this form is not commonly used.


Because rates involve different quantities, and it is essential not to confuse them with ratios.

Instead, rates are usually written using the forward slash, ∕, to separate the terms, with their units clearly specified e.g. $10∕ hour.

Rates are read aloud using the preposition “per”, e.g. $10/ hour is read as “10 dollars per hour”, where “per” just means “for each”.

Why Rates Matter

Many important things in life are rates.

How much you are paid for your labor, either as:

Speed is another rate: the amount of distance in a time period. The time period varies, depending on what we are measuring, for example:

Incidence is another rate: the number of new cases of a disease (in a population) in a period of time.

For chronic conditions, like cancer, we normally assess new cases over a year.

But, when it comes to infectious diseases during a pandemic, we might use a shorter time period, such as weeks or months—even days, if it makes for a good headline!

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