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For smaller numbers, finding the greatest common factor (GCF) is really easy.  You just find all the common factors, like in the last lesson... and pick the biggest one!

(This is also called "greatest common divisor" or "GCD.")

Let's look at some from the last section:

Find the GCF of24and36:
 
1 )List the factors of each:
24 :  1 , 2 , 3 , 4 , 6 , 8 , 12 , 24
36 :  1 , 2 , 3 , 4 , 6 , 9 , 12 , 18 , 36
 
2 )Circle the common factors:
24 :  ( 1 ) , ( 2 ) , ( 3 ) , ( 4 ) , ( 6 ) , 8 , ( 12 ) , 24
36 :  ( 1 ) , ( 2 ) , ( 3 ) , ( 4 ) , ( 6 ) , 9 , ( 12 ) , 18 , 36
 
3 )Grab the greatest common factor
24 :  ( 1 ) , ( 2 ) , ( 3 ) , ( 4 ) , ( 6 ) , 8 , (( 12 )) , 24
36 :  ( 1 ) , ( 2 ) , ( 3 ) , ( 4 ) , ( 6 ) , 9 , (( 12 )) , 18 , 36  ...  12 is the GCF

 

The GCF of 24and36is12.

 

The special math notation for this is

GCF( 24 , 36 ) = 12