07 GCF using Prime Factors Do “07 Warmup GCF with Prime Factors” in clicker (CPS) database. I know how to do prime factorization (factor trees) A=Yes B=No Example : x x Circle if Prime 20 = 2 x 2 x 5

Find GCF 1 st Make Factor Trees for both #’s 2 nd List the prime factors in order for each # 3 rd Multiply the common pairs That’s the GCF !

Example GCF(12,20) = x x Circle if Prime 12 = 2 x 2 x x x 20 = 2 x 2 x 5 Make common pairs x22= 4

Another Example GCF(12,18) = 12 = 2 x 2 x 3 18 = 2 x 3 x 3 x23= 6

Another Example GCF(12,24) = 12 = 2 x 2 x 3 24 = 2 x 2 x 2 x 3 x23 = 12 x2 Notice the GCF is one of the #’s !