The GCF of 8 and 18 is 2. The LCM of 8 and 18 is 72.
Factors of 8: 1, 2, 4, 8.
Factors of 18: 1, 2, 3, 6, 9, 18.
Common factors: 1 and 2. The greatest of these is 2.
8 = 2 × 2 × 2
18 = 2 × 3 × 3
GCF: multiply the prime factors both numbers share: 2 = 2.
LCM: multiply every prime the maximum number of times it appears in either number: 2 × 2 × 2 × 3 × 3 = 72.
Divide the larger number by the smaller and repeat with the remainder until it is 0. The last non-zero remainder is the GCF.
The last non-zero remainder is 2, so GCF(8, 18) = 2.
Multiples of 8: 8, 16, 24, 32, 40, 48, 56, 64, 72, ...
Multiples of 18: 18, 36, 54, 72, 90, ...
The first number in both lists is 72.
2 × 72 = 144 = 8 × 18. This always holds for two numbers, so you can find the LCM as (8 × 18) ÷ 2 = 72.
Divide the top and bottom by the GCF 2: 8/18 = 4/9.
| Numbers | GCF | LCM |
|---|---|---|
| 2 and 8 | 2 | 8 |
| 3 and 8 | 1 | 24 |
| 4 and 8 | 4 | 8 |
| 5 and 8 | 1 | 40 |
| 6 and 8 | 2 | 24 |
| 7 and 8 | 1 | 56 |
| 2 and 18 | 2 | 18 |
| 3 and 18 | 3 | 18 |
| 4 and 18 | 2 | 36 |
| 5 and 18 | 1 | 90 |
| 6 and 18 | 6 | 18 |
| 7 and 18 | 1 | 126 |
See also: factors of 8 · factors of 18 · 8/18 as a decimal.
Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.