6th grade · Math · Unit 1 of 17
Facts & Factors
Facts, primes, GCF and LCM
What your child practices
Quick recall of multiplication and division facts, plus factors, multiples and prime numbers, the greatest common factor (GCF) and least common multiple (LCM), and word problems that use them.
Alabama Course of Study content standard: 6.8 · greatest common factor and least common multiple
How we explain it
Children can open this short lesson before they practice.
- A factor divides a number evenly. 3 and 4 are factors of 12.
- The greatest common factor (GCF) is the biggest factor two numbers share.
- The least common multiple (LCM) is the smallest multiple they share.
Example: Find the GCF of 12 and 18. Factors of 12: 1, 2, 3, 4, 6, 12. Factors of 18: 1, 2, 3, 6, 9, 18. The biggest shared one is 6. Answer: 6
Facts & Factors in Alabama
In the Alabama Course of Study, this is unit 1 of 17 in 6th grade Math, before Mixed Numbers & Ratios.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
What is the greatest common factor (GCF) of 21 and 6?
answer box
3
Hint: List the factors of each number. The GCF is the biggest number that appears in both lists.
Question 2
What is 6 × 5?
6 × 5 = ?
answer box
30
Hint: Split 6 into 5 + 1: 5 × 5 = 25 and 5 × 1 = 5. Add them.
Question 3
What is 40 ÷ 8?
40 ÷ 8 = ?
answer box
5
Hint: Think multiplication: 8 × ? = 40. Which fact do you know?
Question 4
Which number is a multiple of 9?
- 45
- 48
- 47
- 49
45
Hint: A multiple of 9 is in the 9 times table: 9 × 1, 9 × 2, 9 × 3, and so on. Check which choice divides by 9 with nothing left over.
Question 5
What is the least common multiple (LCM) of 3 and 7?
answer box
21
Hint: List multiples of the bigger number: 7, 14, 21… Stop at the first one that 3 also divides into evenly.
Question 6
Which of these numbers is prime?
- 47
- 49
- 51
- 27
47
Hint: A prime number has exactly two factors: 1 and itself. Test each number by dividing by 2, 3, 5 and 7. For example, 27 = 3 × 9, so 27 is not prime.