Name________________________________ Mod____ Date________ LT # _____
PRIME FACTORIZATION METHOD FOR FINDING THE LCM
(LEAST COMMON MULTIPLE) OF TWO NUMBERS
Use prime factorization:
Step 1: Create factor trees for both numbers. Find the prime factorization of both numbers.
Step 2: Find all the common prime factors.
Step 3: Multiply the common prime factors – this will give you the GCF
EX: Find the GCF of 45 and 60.
45 = 3 x 3 x 5
60 = 2 x 2 x 3 x 5
Common prime factors are: 3 and 5 3 x 5 = 15 The GCF=15
LCM = GCF X ALL LEFTOVER PRIMES!
The LCM = 15 x 2 x 2 x 3 = 180
Find the GCF and the LCM of the set of numbers below using prime factorization.
Show all work on loose-leaf paper.
1) 24 and 72 2) 40 and 60
GCF = ____ LCM =_____ GCF = ____ LCM =_____
3) 30 and 36 4) 10 and 15
GCF = ____ LCM =_____ GCF = ____ LCM =_____
