Which one is the Denominator? - Fractions are fun
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Denominators

A pie cut into thirds
A pie cut into thirds

The denominator of a fraction is the number on the bottom (the top is the numerator). In the fraction 1/2, the denominator is 2. In the fraction 45/66, the denominator is 66. In the fraction 2/3, the denominator is 3. For whole numbers, the denominator is always one, so when we say "three", we could also write that as 3/1.

The denominator tells you how many pieces you're cutting your pie into, or how many stops there are between two whole numbers. If the fraction is 1/2, that means you cut the pie into two equal size pieces and then choose one of the pieces: you have one out of two pieces, or half the pie. If the fraction is 1/3, that means you cut the pie into three equal pieces and then choose one of the pieces. You eat one out of three pieces, or a third of the pie.

In order to add or subtract fractions from each other, they need to have a common denominator.

More about numerators
More about common denominators
More about fractions

Bibliography and further reading about numbers:

Fractions
Math
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Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

Professor Carr's PSU page

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