What is GCD(81, 5)?

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

The GCD of 81 and 5 is 1.

How to compute GCD(81, 5)

Comparing the divisors of 81 and 5

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

Divisors of 81:

1, 3, 9, 27, 81

Divisors of 5:

1, 5

We can see from these two lists that the greatest divisor they have in common is: 1

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 81 by 5. The quotient is 16 and the remainder is 1.
  2. The previous divisor (5) is now the dividend. The remainder (1) is the new divisor. Divide 5 by 1. The quotient is 5 and the remainder is 0.
  3. When you reach a remainder of 0, the last divisor (in this case, 1) is the GCD.