



GOOD
NEWS!!! 


This is our last method for finding
common denominators. 





Start
with something like this ... 











STEP 1: 


Break up the denominators into prime
factors ... 











STEP 2: 


List the denominator (Bottom part) prime
factors. 


Write a number the most times it appears in EITHER
fraction. 


This is the common
denominator. 





2 x 2 x 2 x 3 





STEP 3: 


Make fractions equal to 1 to multiply each
fraction in the problem by. 


The
number you build is made up of the common denominator factors 


that
ARE NOT in that denominator. 





In
the first fraction, 


the
denominator is made up of 2 x 3. 


The
common denominator 


is
made up of 2 x 2 x 2 x 3 





The
missing numbers are 2 x 2, 


so
that is what we use in our multiplying fraction. 





Remember
that the multiplying fraction must equal 1. 


That
means we use the same thing on the top and bottom 


of
the multiplying fraction. 











You
can multiply out the numbers in each fraction first 


if you
want to.






Then
multiply the fractions ... 











In
the second fraction, 


the
denominator is made up of 2 x 2 x 2. 


The
common denominator 


is
made up of 2 x 2 x 2 x 3 





The
missing number is 3, 


so
that is what we use in our multiplying fraction. 





Remember
that the multiplying fraction must equal 1. 


That
means we use the same thing on the top and bottom 


of
the multiplying fraction. 











STEP 4: 


Now we have a common denominator so we can
subtract. 











STEP 5: 


Simplify if
possible ... 






Since
the only thing on the top is a 1,
this one can't be simplified. 






copyright 2005 Bruce Kirkpatrick 
