GCF and LCM of 5 and 28

The GCF of 5 and 28 is 1. The LCM of 5 and 28 is 140.

5 and 28 share no common factor except 1, so they are coprime (relatively prime). When two numbers are coprime their LCM is simply their product: 5 × 28 = 140.

Method 1: list the factors (GCF)

Factors of 5: 1, 5.
Factors of 28: 1, 2, 4, 7, 14, 28.
Common factors: 1. The greatest of these is 1.

Method 2: prime factorization

5 = 5 (prime)
28 = 2 × 2 × 7

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: 2 × 2 × 5 × 7 = 140.

Method 3: Euclidean algorithm (GCF)

Divide the larger number by the smaller and repeat with the remainder until it is 0. The last non-zero remainder is the GCF.

  1. 28 = 5 × 5 + 3
  2. 5 = 1 × 3 + 2
  3. 3 = 1 × 2 + 1
  4. 2 = 2 × 1 + 0

The last non-zero remainder is 1, so GCF(5, 28) = 1.

LCM by listing multiples

Multiples of 5: 5, 10, 15, 20, 25, 30, 35, 40, 45, ...
Multiples of 28: 28, 56, 84, 112, 140, 168, ...
The first number in both lists is 140.

Check: GCF × LCM = product

1 × 140 = 140 = 5 × 28. This always holds for two numbers, so you can find the LCM as (5 × 28) ÷ 1 = 140.

Simplifying the fraction 5/28

5/28 is already in lowest terms because the GCF of 5 and 28 is 1.

GCF and LCM of similar pairs

NumbersGCFLCM
2 and 5110
3 and 5115
4 and 5120
5 and 6130
5 and 7135
5 and 8140
2 and 28228
3 and 28184
4 and 28428
6 and 28284
7 and 28728
8 and 28456

See also: factors of 5 · factors of 28.

Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.