The rule of three is used to solve problems of proportionality.

I bought one or two books yesterday.

They decided to form ménages à trois.

They explored the complex dynamics of a ménage
trois during an open and honest conversation.

There are eighty-three days in this year.

She paid next to nothing for this painting.

Never two without three, it's always like that.

He bought this old book for peanuts.

The common hepatica is a species of perennial herbaceous plant with three lobes.

She is as tall as three apples.