The GCF of 5 and 15 is 5. The LCM of 5 and 15 is 15.
Factors of 5: 1, 5.
Factors of 15: 1, 3, 5, 15.
Common factors: 1 and 5. The greatest of these is 5.
5 = 5 (prime)
15 = 3 × 5
GCF: multiply the prime factors both numbers share: 5 = 5.
LCM: multiply every prime the maximum number of times it appears in either number: 3 × 5 = 15.
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 5, so GCF(5, 15) = 5.
Multiples of 5: 5, 10, 15, 20, ...
Multiples of 15: 15, 30, ...
The first number in both lists is 15.
5 × 15 = 75 = 5 × 15. This always holds for two numbers, so you can find the LCM as (5 × 15) ÷ 5 = 15.
Divide the top and bottom by the GCF 5: 5/15 = 1/3.
| Numbers | GCF | LCM |
|---|---|---|
| 2 and 5 | 1 | 10 |
| 3 and 5 | 1 | 15 |
| 4 and 5 | 1 | 20 |
| 5 and 6 | 1 | 30 |
| 5 and 7 | 1 | 35 |
| 5 and 8 | 1 | 40 |
| 2 and 15 | 1 | 30 |
| 3 and 15 | 3 | 15 |
| 4 and 15 | 1 | 60 |
| 6 and 15 | 3 | 30 |
| 7 and 15 | 1 | 105 |
| 8 and 15 | 1 | 120 |
See also: factors of 5 · factors of 15 · 5/15 as a decimal.
Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.