07 GCF using Prime FactorsDo “07 Warmup GCF with Prime Factors” in clicker (CPS) database.

I know how to do prime factorization (factor trees) A=Yes B=No

20

4 5

2 2

Example:

x

x

Circle if Prime

20 = 2 x 2 x 5

Find GCF1st Make Factor Trees for both #’s

2nd List the prime factors in order for each #

3rd Multiply the common pairs

That’s the GCF !

Example

GCF(12,20) =

20

4 5

2 2

x

x

Circle if Prime

12 = 2 x 2 x 3

12

4 3

2 2

x

x

20 = 2 x 2 x 5

Make common pairs

x2 2 = 4

Another Example

GCF(12,18) =

12 = 2 x 2 x 3

18 = 2 x 3 x 3

x2 3 = 6

Another Example

GCF(12,24) =

12 = 2 x 2 x 3

24 = 2 x 2 x 2 x 3

x2 3 = 12x2

Notice the GCF is one of the #’s !