WHAT IS A COMMON DENOMINATOR AND WHY IS ONE NECESSARY?

To be able to add things, the things have to be like each other.  Like means identical in size and shape.

      
These squares can not be added together since they are not like each other.

These squares can be added together since they are like each other.

Now for fractions.   

• Remember that to create a fraction, a whole must be cut into equal pieces.
• The denominator of a fraction tells the number of equal pieces in the whole.
• Fractions with the same denominator have pieces that are like each other.
• Selected pieces can be added if they are like each other.
• Fractions can be added if they are like each other.
• Fractions are like each other if their denominators are the same.
• Fractions with the same denominator are said to have common denominators.

Listen to that again! 

• Fractions can only be added if they are like each other.
• That means they have common denominators.

To add like fractions, just add the numerators and keep the common denominator.

You should be able to work these examples!                

Review this material until you are able to answer these questions.

• What does it mean when things are like each other?
• When are fractions like each other?
• When can fractions be added?

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