Grade 4 Factors & Multiples: Greatest Common Factor

Find GCF of two numbers

What You'll Learn

List the factors of both numbers
Find the factors they share (1 is always one)
Pick the greatest shared factor

📖GCF

The GCF is the largest factor they share! 12: 1, 2, 3, 4, 6, 12. 18: 1, 2, 3, 6, 9, 18. Shared: 1, 2, 3, 6 — so the GCF of 12 and 18 is 6.

💡Where this fits

Common Core teaches the greatest common factor in grade 6 (6.NS.B.4), so this lesson is a stretch for this grade. In grade 4 it builds on listing factor pairs for numbers up to 100 (4.OA.B.4), so every number here is 60 or less.

Worked examples

Real problems from the practice worksheets, solved one step at a time.

Example 1
What is the greatest common factor (GCF) of 44 and 26?
1. The factors of 44 are 1, 2, 4, 11, 22, 44.
2. The factors of 26 are 1, 2, 13, 26.
3. The factors they share are 1, 2. The greatest one is 2.
4. The GCF of 44 and 26 is 2.
Answer: 2
Example 2
What is the greatest common factor (GCF) of 10 and 18?
1. The factors of 10 are 1, 2, 5, 10.
2. The factors of 18 are 1, 2, 3, 6, 9, 18.
3. The factors they share are 1, 2. The greatest one is 2.
4. The GCF of 10 and 18 is 2.
Answer: 2
Example 3
What is the greatest common factor (GCF) of 44 and 36?
1. The factors of 44 are 1, 2, 4, 11, 22, 44.
2. The factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, 36.
3. The factors they share are 1, 2, 4. The greatest one is 4.
4. The GCF of 44 and 36 is 4.
Answer: 4