What is GCD(8, 20)?

The GCD (Greatest Common Divisor) is the largest number that can divide two (or more) numbers without leaving a remainder.

The GCD of 8 and 20 is 4.

How to compute GCD(8, 20)

Comparing the divisors of 8 and 20

This first method consists in listing the divisors of the two numbers and then identifying the largest one they have in common.

Divisors of 8:

1, 2, 4, 8

Divisors of 20:

1, 2, 4, 5, 10, 20

We can see from these two lists that the greatest divisor they have in common is: 4

For small numbers, this can be done quickly. However, as numbers increase, the list of potential divisors grows longer, making this method cumbersome and less practical.

Euclid's algorithm

Fortunately, there's a much more efficient method: Euclid's algorithm. It's particularly well-suited to larger numbers. Here's how it works:

  1. Divide 20 by 8. The quotient is 2 and the remainder is 4.
  2. The previous divisor (8) is now the dividend. The remainder (4) is the new divisor. Divide 8 by 4. The quotient is 2 and the remainder is 0.
  3. When you reach a remainder of 0, the last divisor (in this case, 4) is the GCD.