The highest common factor (HCF) of two numbers is the biggest number that divides both. The factors of 18 are 1, 2, 3, 6, 9, 18 and of 24 are 1, 2, 3, 4, 6, 8, 12, 24. The HCF is 6.
The lowest common multiple (LCM) is the smallest number in both times tables. Multiples of 6 are 6, 12, 18, 24 and multiples of 8 are 8, 16, 24. The LCM is 24. The HCF helps simplify fractions, and the LCM helps find common denominators.
Worked example
Find the HCF of 36 and 45.
- Factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36.
- Factors of 45: 1, 3, 5, 9, 15, 45. The biggest in both is 9.
Answer:9
Key words
- HCF
- highest common factor
- LCM
- lowest common multiple
- common
- shared by both numbers
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Common Core-referenced: 6.NS.B.4