Denominator: Definition & Concept

Instructor: Jennifer Beddoe

Jennifer has an MS in Chemistry and a BS in Biological Sciences.

Fractions are used to describe a part of something and are comprised of a numerator (the top part) and the denominator (the bottom part). This lesson will go into more detail about the denominator and will conclude with a quiz to test your knowledge.


Fractions are part of our lives, and most people use them on a daily basis - sometimes without even knowing it. What would life be like without fractions? There would be no way to tell your friends how fat you feel because you ate half a gallon of ice cream for dinner last night. Coin money would cease to exist; what is a quarter but 1/4 of a dollar?

There are three parts to every fraction:

  • The numerator, the number on top of the fraction
  • The denominator, the number on bottom of the fraction
  • The line dividing the two


Why Denominator?

'Numerator' is a Latin word that means 'number.' This is because it represents the number of parts. 'Denominator' is also Latin and means 'namer.' It is the portion of the fraction that names or defines the whole. These words were first used to describe fractions by 13th-century mathematicians.

The word fraction comes from the Latin 'fractus,' which means broken. A fraction describes a portion of something that has been broken into pieces. The numerator is how many pieces, and the denominator describes how many pieces make up the whole. So, if you eat 5/8 of a pizza, that really means that the pizza was cut into 8 pieces and you ate 5 of them.


If you're having trouble remembering which part of the fraction is the denominator, here's a helpful trick: the words 'denominator' and 'down' both start with 'd.' So, the denominator is the 'down,' or bottom, part of the fraction.

Types of Fractions

There are three different types of fractions:

  • Proper fractions are written in the proper from - the numerator is smaller than the denominator, and they cannot be simplified any further.
  • Improper fractions are ones in which the numerator is greater than the denominator.
  • Mixed fractions combine a whole number and a proper fraction. With a mixed fraction, you have at least one of something and also a part of another one. For example, 'the soccer team ate 3 1/2 pizzas at the party.'


Denominator Requirements

Almost anything can be in the denominator of a fraction: positive or negative numbers, letters, variables, or even whole equations. Some fractions are very complex, like this one:


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