Greatest Common Factors a.k.a. GCF

Greatest Common Factors• When two numbers share a factor, that

factor is called a common factor.– Factors of 8: 1, 2, 4, 8– Factors of 12: 1, 2, 3, 4, 6, 12– The common factors of 8 and 12 are 1, 2, and

4.• The greatest common factor is the largest

factor shared by two or more numbers.– The greatest common factor of 8 and 12 is 4.

ExamplesFind the common factors and greatest common factor of 10, 20, and 30.• First list the factors of each number.– factors of 10: ________________________– factors of 20: ________________________– factors of 30: ________________________

• Then list all of the common factors: ___________• Finally, compare these factors to find the greatest

common factor: __________

TOTD 1/8/15List all the factors of each number and then identify the number as prime or composite.1) 35:_______________ P or C2) 51: _______________ P or CList the factors of each number. Then find the greatest common factor of the numbers.3) 12, 14: ___________________GCF ____________4) 6, 21: ____________________GCF ____________Multiply. 5) 8.91 x 3.2Divide. 6) 31.05 ÷ .9