GCF / LCM Using Prime Factorization Tip to Remember: GCF should have a short string (only the shared factors) – factors are small LCM should have a long string (shared factors times unused factors) – multiples are large

GCF Remember that factor (which sounds like ‘fraction’) is smaller; this means that we will only use the shared prime factors the smaller string. 12: 2 x 2 x 3 20: 2 x 2 x 5 The only thing shared between the two numbers are 2 x 2. That means that the GCF is 2 x 2. GCF = 4

LCM Remember that Multiple sounds like multiplication, so you are looking for a big number and a big string. 12: 2 x 2 x 3 20: 2 x 2 x 5 Only use shared numbers one time. Then multiply any unused numbers LCM = 2 x 2 x 3 x 5 LCM = 60