Math Antics
Prime Factorization
Break any number into its prime building blocks — the key to GCF and LCM.
Watch on YouTubeNumbers that divide in, numbers you count by, and the values they share.
Read this first — it covers the idea in plain language with a worked example.
A factor is a number that divides evenly into another number, leaving no remainder. The factors of 12 are 1, 2, 3, 4, 6, and 12, because each one divides 12 exactly.
A multiple is what you get when you skip-count by a number. The multiples of 4 are 4, 8, 12, 16, 20, and so on. Notice that every number is a factor of its own multiples.
The GCF of two numbers is the largest factor they share. List the factors of each number, then pick the biggest one that appears in both lists.
Find the GCF of 18 and 24.
The LCM is the smallest multiple that two numbers share. Skip-count by each number until you reach the first value they both land on.
Find the LCM of 6 and 8.
Tip
For larger numbers, break each one into primes (prime factorization) — it makes finding the GCF and LCM much faster.
A short video that walks through this topic.
Break any number into its prime building blocks — the key to GCF and LCM.
Watch on YouTubeTry a worksheet or work through some problems before the quiz.
A couple of questions to make sure this topic stuck. Retake as many times as you want.
Factors, Multiples, GCF & LCM
What is the GCF of 18 and 24?