How it works
The greatest common factor is the biggest number that goes into both.
You can write a sum as a common factor times a sum: 20 + 8 = 4 × (5 + 2).
The common factor comes out of the brackets.
Worked examples
Fill the gap
- 20 + 8 = 4 × (? + 2).
- 4 × 5 = 20 and 4 × 2 = 8, so the gap is 5.
- 20 + 8 = 4 × (5 + 2).
Another
- 30 + 18 = 6 × (? + 3).
- 6 × 5 = 30 and 6 × 3 = 18, so the gap is 5.
- 30 + 18 = 6 × (5 + 3).
Find the greatest factor
- 24 + 78.
- 6 goes into 24 and 78. 24 ÷ 6 = 4 and 78 ÷ 6 = 13.
- 24 + 78 = 6 × (4 + 13).
A taste of the worksheet
These are the first problems of set A. The printable sheet has many more, with an answer key.
- Sensei packs 6 red counters and 10 blue counters into matching bags. Every bag has the same mix and nothing is left over. What is the most bags? ___
- The lists show every factor of 15 and of 24. What is the greatest common factor of 15 and 24? ___
- Circle every common factor of 12 and 18.
- The lists show the first multiples of 4 and of 6. What is the least common multiple of 4 and 6? ___