The GCF of 15 and 25 is 5. The LCM of 15 and 25 is 75.
Factors of 15: 1, 3, 5, 15.
Factors of 25: 1, 5, 25.
Common factors: 1 and 5. The greatest of these is 5.
15 = 3 × 5
25 = 5 × 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 × 5 = 75.
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(15, 25) = 5.
Multiples of 15: 15, 30, 45, 60, 75, 90, ...
Multiples of 25: 25, 50, 75, 100, ...
The first number in both lists is 75.
5 × 75 = 375 = 15 × 25. This always holds for two numbers, so you can find the LCM as (15 × 25) ÷ 5 = 75.
Divide the top and bottom by the GCF 5: 15/25 = 3/5.
| Numbers | GCF | LCM |
|---|---|---|
| 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 |
| 7 and 15 | 1 | 105 |
| 2 and 25 | 1 | 50 |
| 3 and 25 | 1 | 75 |
| 4 and 25 | 1 | 100 |
| 5 and 25 | 5 | 25 |
| 6 and 25 | 1 | 150 |
| 7 and 25 | 1 | 175 |
See also: factors of 15 · factors of 25.
Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.