GCF LCM Math Tips

Remember that you can find the GCF 2 different ways.
1. You can list all of the factors of each number
                        20 = (1,2, 4, 5, 10, 20) and 30 = 1, 2, 3, 5, 6, 10, 15, 30) GCF = 10
2. you can use prime factorization


20 when using prime factorization = 2 x 2 x 5           and 30 when using prime factorization = 2 x 3 x 5

you simply sort them then multiply the prime factors they have in common

20 prime                           common                         30 prime
   2                                          2                                       3
                                               5

2 x 5 = 10 GCF = 10

Remember you can also find the LCM two ways also
1. you can skip count until you reach a match
                   20 = 20, 40, 60, 80, 100
                   30 = 30, 60, 90, 120, 150
LCM = 60

2. you can use prime factorization


you simply sort the prime factors then multiply all of the numbers together.
20 prime                          common                            30 prime
 2                                          2                                        3
                                             5
2 x 2 x 5 x 3 = 60 LCM = 60