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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.