The GCF of 4 and 40 is 4. The LCM of 4 and 40 is 40.
Factors of 4: 1, 2, 4.
Factors of 40: 1, 2, 4, 5, 8, 10, 20, 40.
Common factors: 1, 2 and 4. The greatest of these is 4.
4 = 2 × 2
40 = 2 × 2 × 2 × 5
GCF: multiply the prime factors both numbers share: 2 × 2 = 4.
LCM: multiply every prime the maximum number of times it appears in either number: 2 × 2 × 2 × 5 = 40.
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 4, so GCF(4, 40) = 4.
Multiples of 4: 4, 8, 12, 16, 20, 24, 28, 32, 36, ...
Multiples of 40: 40, 80, ...
The first number in both lists is 40.
4 × 40 = 160 = 4 × 40. This always holds for two numbers, so you can find the LCM as (4 × 40) ÷ 4 = 40.
Divide the top and bottom by the GCF 4: 4/40 = 1/10.
| Numbers | GCF | LCM |
|---|---|---|
| 2 and 4 | 2 | 4 |
| 3 and 4 | 1 | 12 |
| 4 and 5 | 1 | 20 |
| 4 and 6 | 2 | 12 |
| 4 and 7 | 1 | 28 |
| 4 and 8 | 4 | 8 |
| 2 and 40 | 2 | 40 |
| 3 and 40 | 1 | 120 |
| 5 and 40 | 5 | 40 |
| 6 and 40 | 2 | 120 |
| 7 and 40 | 1 | 280 |
| 8 and 40 | 8 | 40 |
See also: factors of 4 · factors of 40.
Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.