- Definition
The greatest common factor is the biggest number that divides evenly into two or more other numbers. For example, the biggest number that divides into both 16 and 24 is 8.
To find the greatest common factor of 12 and 18, we see their common factors are 1, 2, 3, and 6, making 6 the greatest.
How to teach this in 30 seconds
Try this analogy: The greatest common factor is like finding the largest size of identical teams you can make from two different groups of kids, with no one left over.
Ask your child: What numbers can you divide evenly into both 12 and 16?
Common mix-up: Kids often confuse this with finding a multiple, which makes the number bigger. The greatest common factor is always smaller than or equal to the smallest of the original numbers.
Examples
- The greatest common factor of 15 and 25 is 5, because 5 is the largest number that divides into both.
- For 7 and 14, the greatest common factor is 7.
greatest common factor is a term used in Ontario’s Kindergarten to Grade 8 curriculum.
Where this shows up
The descriptions on this page are SmartStudy’s own original, plain-language writing — not the Ministry’s wording. They are aligned to the Ontario Curriculum, © King’s Printer for Ontario. For the Ministry’s official wording, see the source link below. SmartStudy is an independent service and is not affiliated with, endorsed by, or sponsored by the Government of Ontario or the Ministry of Education. Ontario Curriculum and Resources ↗
