The GCF of 6 and 15 is 3. The LCM of 6 and 15 is 30.
Factors of 6: 1, 2, 3, 6.
Factors of 15: 1, 3, 5, 15.
Common factors: 1 and 3. The greatest of these is 3.
6 = 2 × 3
15 = 3 × 5
GCF: multiply the prime factors both numbers share: 3 = 3.
LCM: multiply every prime the maximum number of times it appears in either number: 2 × 3 × 5 = 30.
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 3, so GCF(6, 15) = 3.
Multiples of 6: 6, 12, 18, 24, 30, 36, ...
Multiples of 15: 15, 30, 45, ...
The first number in both lists is 30.
3 × 30 = 90 = 6 × 15. This always holds for two numbers, so you can find the LCM as (6 × 15) ÷ 3 = 30.
Divide the top and bottom by the GCF 3: 6/15 = 2/5.
| Numbers | GCF | LCM |
|---|---|---|
| 2 and 6 | 2 | 6 |
| 3 and 6 | 3 | 6 |
| 4 and 6 | 2 | 12 |
| 5 and 6 | 1 | 30 |
| 6 and 7 | 1 | 42 |
| 6 and 8 | 2 | 24 |
| 2 and 15 | 1 | 30 |
| 3 and 15 | 3 | 15 |
| 4 and 15 | 1 | 60 |
| 5 and 15 | 5 | 15 |
| 7 and 15 | 1 | 105 |
| 8 and 15 | 1 | 120 |
See also: factors of 6 · factors of 15 · 6/15 as a decimal.
Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.