How to Find Factors, GCF, and LCM
Factors go INTO a number. Multiples come FROM a number.
1.Find the factors
Factors are numbers that multiply together to make a number.
Example: factors of 12
1 × 12 = 122 × 6 = 123 × 4 = 12
Write every number you used:
1, 2, 3, 4, 6, 12
2.GCF
GCF = Greatest Common Factor
List the factors of BOTH numbers.
12: 1, 2, 3, 4, 6, 12
18: 1, 2, 3, 6, 9, 18
Circle the numbers in BOTH lists: 1, 2, 3, 6
The biggest one is 6. GCF = 6
Use GCF to simplify fractions:
1218÷ 6 →23Done.
3.LCM
LCM = Least Common Multiple
Count by BOTH numbers.
4: 4, 8, 12, 16, 20, 24…
6: 6, 12, 18, 24…
The first number in BOTH lists is 12.
LCM = 12
Use LCM to get matching bottoms for + or −:
14+16→312+212=512