Greatest Common Divisor (GCD) of 21 and 18
The greatest common divisor (GCD) of 21 and 18 is 3.
What is the Greatest Common Divisor (GCD)?
The GCD of two integers is the largest positive integer that divides both numbers without leaving a remainder. It is useful in simplifying fractions, finding common factors, and in number theory.
How to Calculate the GCD of 21 and 18?
We use the Euclidean algorithm, which involves the following steps:
- Divide the larger number by the smaller number.
- Replace the larger number with the smaller number and the smaller number with the remainder from the division.
- Repeat this process until the remainder is zero.
- The non-zero remainder just before zero is the GCD.
Step-by-Step Euclidean Algorithm
| Step | Calculation |
|---|---|
| 1 | 21 ÷ 18 = 1 remainder 3 |
| 2 | 18 ÷ 3 = 6 remainder 0 |
Examples of GCD Calculations
| Numbers | GCD |
|---|---|
| 84 and 123 | 3 |
| 166 and 117 | 1 |
| 70 and 109 | 1 |
| 120 and 124 | 4 |
| 32 and 51 | 1 |