To find the greatest common factor of two numbers, you first have to list each number's factors quickly — and that runs on multiplication facts and knowing what divides evenly. Get these warm and GCF feels easy.
Answer these 3, then press Show my path. No grade — this just points you to the right level.
1. What is 6 × 7?
2. Which number is a factor of 12 (divides it evenly)?
3. Is 15 divisible by 3 (no remainder)?
A factor of a number divides it evenly (no remainder). To list factors, find every pair that multiplies to the number.
Your quick check picks one for you, but you can switch any time:
Level 0 Let's list factors one step at a time.
A. Fill the missing partner: 1 × ___ = 6
What times 1 gives 6? 1 × 6 = 6.
B. Fill the missing partner: 2 × ___ = 6
2 × 3 = 6.
C. So the factors of 6 are 1, 2, 3, and ___?
Every number is a factor of itself: 6.
Level 1 List the factors, then spot the shared ones.
A. How many factors does 8 have? (1, 2, 4, 8)
Pairs: 1×8 and 2×4 → four factors: 1, 2, 4, 8.
B. Which number is a common factor of 8 and 12?
Factors of 8: 1,2,4,8. Factors of 12: 1,2,3,4,6,12. They share 1, 2, and 4.
Level 2 Warm-up straight into GCF.
A. Factors of 18 and 24 — what is the greatest factor they share?
18: 1,2,3,6,9,18. 24: 1,2,3,4,6,8,12,24. Shared: 1,2,3,6 → greatest is 6.
B. What is the GCF of 9 and 15?
9: 1,3,9. 15: 1,3,5,15. Greatest shared = 3.
1. List a factor of 10 that is greater than 1 and less than 10.
10 = 2 × 5, so 2 and 5 are factors.
2. What is the greatest common factor of 6 and 9?
6: 1,2,3,6. 9: 1,3,9. Greatest shared = 3.
You've practiced exactly what Lesson 1-2 uses. Time to dive in.
Start Lesson 1-2 →