The GCF of 7 and 15 is 1. The LCM of 7 and 15 is 105.
7 and 15 share no common factor except 1, so they are coprime (relatively prime). When two numbers are coprime their LCM is simply their product: 7 × 15 = 105.
Factors of 7: 1, 7.
Factors of 15: 1, 3, 5, 15.
Common factors: 1. The greatest of these is 1.
7 = 7 (prime)
15 = 3 × 5
GCF: multiply the prime factors both numbers share: there are none, so the GCF is 1.
LCM: multiply every prime the maximum number of times it appears in either number: 3 × 5 × 7 = 105.
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 1, so GCF(7, 15) = 1.
Multiples of 7: 7, 14, 21, 28, 35, 42, 49, 56, 63, ...
Multiples of 15: 15, 30, 45, 60, 75, 90, 105, 120, ...
The first number in both lists is 105.
1 × 105 = 105 = 7 × 15. This always holds for two numbers, so you can find the LCM as (7 × 15) ÷ 1 = 105.
7/15 is already in lowest terms because the GCF of 7 and 15 is 1.
| Numbers | GCF | LCM |
|---|---|---|
| 2 and 7 | 1 | 14 |
| 3 and 7 | 1 | 21 |
| 4 and 7 | 1 | 28 |
| 5 and 7 | 1 | 35 |
| 6 and 7 | 1 | 42 |
| 7 and 8 | 1 | 56 |
| 2 and 15 | 1 | 30 |
| 3 and 15 | 3 | 15 |
| 4 and 15 | 1 | 60 |
| 5 and 15 | 5 | 15 |
| 6 and 15 | 3 | 30 |
| 8 and 15 | 1 | 120 |
See also: factors of 7 · factors of 15 · 7/15 as a decimal.
Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.