Worked examples
Two examples
Example 1
The greatest common factor of 18 and 24 is
- Factors of 18: 1, 2, 3, 6, 9, 18.
- Factors of 24: 1, 2, 3, 4, 6, 8, 12, 24.
- The largest number in both lists is 6.
Answer: 6
Example 2
The greatest common factor of 15 and 28 is
- Factors of 15: 1, 3, 5, 15. Factors of 28: 1, 2, 4, 7, 14, 28.
- The only number in both lists is 1.
Answer: 1
Where this is taught: Quiz 7: Factors, Multiples, and Primes, “Finding every factor: the pair walk”
The drill
Ten problems
This drill also has challenge problems. They use the same skill, set up the way the GED test sometimes sets up a problem, so that it looks new at first.
How many:
Type each answer, then press Check my answers at the bottom. Commas in large numbers are fine.Write each answer on the line. The answer key, with the reasoning, is on the last page.