Finding the greatest common divisor (GCD) of a group of numbers can be simple, but you need to know how. To find the greatest common divisor of two numbers, you need to know how to factor both numbers.
Steps
Method 1 of 2: Method One: Compare Common Factors
Step 1. You need to know that you can find the greatest common factor simply by comparing the factors by which the number can be divided
You don't need to know prime factorization to do this. Start by finding all the factors of the group of numbers you are comparing.
Step 2. Compare the groups of factors until you find the largest one that is in both groups
Step 3. This is the greatest common factor
Method 2 of 2: Method Two: Using Prime Numbers
Step 1. Break each number into prime numbers
A prime number is a number greater than 1 that is divisible only by 1 and itself. Examples of prime numbers are 5, 17, 97 and 331, just to name a few.
Step 2. Identify common prime factors
Highlight all prime factors common to both groups of numbers. There could be several.
Step 3. Calculate:
if there is only one common prime factor, then that is the greatest common factor. If there are more, multiply them together to get the greatest common divisor.
Step 4. Study this example
To demonstrate this method, cover this example.
Advice
- A prime number is a number greater than 1 that can only be divided by 1 and by itself.
- Did you know that the 3rd century AD mathematician Euclid has created an algorithm to find the greatest common divisor in the case of two natural numbers or two polynomials?
