6th grade · Math · Unit 1 of 21
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.
New York State Learning Standards learning standard: NY-6.NS.4 · 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 New York
In the New York State Learning Standards, this is unit 1 of 21 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
Two lights blink together. One blinks every 9 seconds and the other every 5 seconds. After how many seconds will they next blink at the same time?
- 45
- 14
- 9
- 90
45
Hint: You need a number that is a multiple of both 9 and 5. Find the least common multiple.
Question 2
What number goes in the box?
3 × = 12
- 4
- 6
- 3
- 2
4
Hint: Divide to find a missing factor: 12 ÷ 3.
Question 3
Which number is a factor of 60?
- 13
- 8
- 12
- 9
12
Hint: A factor divides 60 with no remainder. Try dividing 60 by each choice. For example, 60 ÷ 12 = 5 exactly.
Question 4
What is 48 ÷ 8?
48 ÷ 8 = ?
answer box
6
Hint: Think multiplication: 8 × ? = 48. Which fact do you know?
Question 5
What is the least common multiple (LCM) of 4 and 7?
answer box
28
Hint: List multiples of the bigger number: 7, 14, 21… Stop at the first one that 4 also divides into evenly.
Question 6
Which of these numbers is prime?
- 41
- 27
- 39
- 57
41
Hint: A prime number has exactly two factors: 1 and itself. Test each number by dividing by 2, 3, 5 and 7. For example, 39 = 3 × 13, so 39 is not prime.