Greatest Common Divisor (GCD) of 15 and 81
The greatest common divisor (GCD) of 15 and 81 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 15 and 81?
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 | 15 ÷ 81 = 0 remainder 15 |
| 2 | 81 ÷ 15 = 5 remainder 6 |
| 3 | 15 ÷ 6 = 2 remainder 3 |
| 4 | 6 ÷ 3 = 2 remainder 0 |
Examples of GCD Calculations
| Numbers | GCD |
|---|---|
| 195 and 184 | 1 |
| 25 and 165 | 5 |
| 78 and 13 | 13 |
| 185 and 92 | 1 |
| 145 and 18 | 1 |