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GREATEST COMMON FACTOR

Here's another Number Trick from one of my students.   Unfortunately, I am unable to print his name on the internet.  However, he does know who he is and I thank him very much! This is a very useful trick to use when trying to figure out GREATEST COMMON FACTOR or GCF.  So teachers take note.  This tricks works quite well.

Step 1:   First make an L shape (like an upside down long division sign) and put both numbers inside. For example: the GCF of 9 and 12.

Step 2:   Find a PRIME number that can evenly divide into both numbers.  Place that number on the left of the figure.

Step 3:   Then divide the number and place the answers under the numbers. If the numbers still have a common factor then repeat steps 1-3, using only PRIME numbers.

Step 4:   Multiply all number that are outside on the left of the figure and that will be the GCF.

Here's a second example:

The GCF of 30 and 75.  Here I had to repeat steps 1-3.

Here's a third example:

The GCF of 24, 64, and104.  Here I had to repeat steps 1-3 twice.