Total Fabrication

Glossary

How do you add, subtract, multiply and divide fractions?

Adding fractions

You can add fractions if the denominators are the same. You simply add the numerators.

Example:     1 sixteenth + 3 sixteenths + 5 sixteenths = 9 sixteenths

If the fractions have different denominators, determine the lowest common denominator (LCD) so that you can express each fraction in equivalent form. The lowest common denominator is the lowest number that the denominator of each individual fraction will divide into.

Example:     Demonstrating how to find the lowest common denominator

Mixed numbers need to be converted to improper fractions before using this addition technique.

Converting mixed numbers to improper fractions

Subtracting fractions

Subtracting fractions is very similar to adding in that all fractions in your calculation need to have the same denominator. You may need to determine the lowest common denominator (LCD) as you did with addition.

Example:
     Subtracting fractions example

Multiplying fractions

Multiplication of fractions is carried out by multiplying all the numerators together and all the denominators together.

Example:     2 over 5 times 3 over 7 = 2 time 3 over 5 times 7 = 6 over 35

Sometimes the answer to a multiplication calculation can be simplified by dividing both numerator and denominator by the same number. This process is called cancelling, because you strike out the original numbers to create the new fraction.

Example:     15 over 25. Divide numerator and denominator by 5.  Equals 3 over 5

Dividing fractions

To divide by a fraction, invert it and multiply.

Example:   
  Demonstrates how to divide a fraction by inverting and multiplying

Demonstrates how to divide a fraction by inverting and multiplying

 

Need more practice?

Word iconComplete this fractions activity sheet (Word 93 kb)

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