The GCF of 10 and 20 is 10. The LCM of 10 and 20 is 20.
Factors of 10: 1, 2, 5, 10.
Factors of 20: 1, 2, 4, 5, 10, 20.
Common factors: 1, 2, 5 and 10. The greatest of these is 10.
10 = 2 × 5
20 = 2 × 2 × 5
GCF: multiply the prime factors both numbers share: 2 × 5 = 10.
LCM: multiply every prime the maximum number of times it appears in either number: 2 × 2 × 5 = 20.
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 10, so GCF(10, 20) = 10.
Multiples of 10: 10, 20, 30, ...
Multiples of 20: 20, 40, ...
The first number in both lists is 20.
10 × 20 = 200 = 10 × 20. This always holds for two numbers, so you can find the LCM as (10 × 20) ÷ 10 = 20.
Divide the top and bottom by the GCF 10: 10/20 = 1/2.
| Numbers | GCF | LCM |
|---|---|---|
| 2 and 10 | 2 | 10 |
| 3 and 10 | 1 | 30 |
| 4 and 10 | 2 | 20 |
| 5 and 10 | 5 | 10 |
| 6 and 10 | 2 | 30 |
| 7 and 10 | 1 | 70 |
| 2 and 20 | 2 | 20 |
| 3 and 20 | 1 | 60 |
| 4 and 20 | 4 | 20 |
| 5 and 20 | 5 | 20 |
| 6 and 20 | 2 | 60 |
| 7 and 20 | 1 | 140 |
See also: factors of 10 · factors of 20 · 10/20 as a decimal.
Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.