Finding a common denominator

	The addition and subtraction of fractions
	Fractions

1. Finding a common denominator for the fractions.

Let's look at the name of the parts of a fraction:

Numerator means that it enumerates, that is, it indicates the number of parts you have.

Denominator means that it designates, that is, it shows you the number of parts the whole is divided into. Having halves is not the same as having thirds.

When you add up, you add homogeneous elements, they have to be quantities of the same thing. Then, in order to have fractions, they must be of the same kind, all of them must have the same denominator.

If the fractions have different denominators, you have to find a common denominator, that is, they are changed by other equivalent fractions but all with the same denominator.

In this window you can observe the reason for finding a common denominator for fractions.
Two fractions and its graphical representations are shown on the left.
When you click on the blue triangle, the fractions and its graphical representations are transformed into equivalent fractions, but both with the same denominator.
The new fractions are marked in grey so that you can compare them with the previous ones.
If you click on the red triangle, they return to their previous state.
When you click on Init other fractions will appear.

	Eduardo Barbero Corral

	Spanish Ministry of Education. Year 2007

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