Question

Find the greatest common factor. $$30,45$$

Short answer

Therefore, the greatest common factor of 30 and 45 is 15.

Step-by-step solution

Prime Factorization of Numbers

First, start with finding the prime factors of both numbers. The prime factors of 30 are: \(2, 3, 5\). The prime factors of 45 are: \(3, 3, 5\).

Identify common prime factors

Next step is to identify the common prime factors between the two numbers. The common prime factors of 30 and 45 are: \(3, 5\).

Multiply Common Factors

Finally, to find the greatest common factor, multiply all the common prime factors together. So, \(3*5 = 15\).

Key concepts

Prime Factorization

Understanding prime factorization is crucial for finding the greatest common factor (GCF). It involves breaking down a number into the set of prime numbers that, when multiplied together, equal the original number. Prime numbers are those that have only two distinct positive divisors: 1 and the number itself.

For example, when we look at the number 30, its prime factors are 2, 3, and 5. These are all prime because no other numbers can divide them evenly apart from 1 and themselves. To perform prime factorization, we often use a factor tree:\

• Start with the number 30.
• Divide by the smallest prime number that can divide evenly, which is 2.
• Now we have 15, which is not divisible by 2, so we move to the next smallest prime, 3.
• Dividing 15 by 3 gives us 5, which is also a prime number.
• End the process since 5 can only be divided evenly by 1 or 5.

This process results in 30 being expressed as the product of its prime factors:

\(2 \times 3 \times 5\text{.}\)

Common Prime Factors

Once prime factorization of the given numbers is completed, the next step for finding the GCF is to identify the common prime factors. These are the prime numbers that appear in the prime factorization of both numbers.

Let's consider our example numbers 30 and 45. From the prime factorization, we find that the prime factors of 30 are 2, 3, and 5, while the prime factors of 45 are 3, 3, and 5. The common prime factors are clearly 3 and 5, since these are the primes shared by both 30 and 45. It's also important to note that we use each common prime factor only once when calculating the GCF, even if it appears multiple times in the factorization of one number.

Multiplying Factors

The last step in finding the greatest common factor is to multiply the common prime factors identified in the previous step. Multiplication is one of the basic arithmetic operations and can be thought of as repeated addition. Here, it serves as a way to combine the common primes into a single number, which represents the largest divisor shared by both numbers in question.

In our case with the numbers 30 and 45, after extracting the common prime factors 3 and 5, we multiply them together:\
\(3 \times 5 = 15\text{.}\)

The product, 15, represents the greatest common factor of 30 and 45. This means that 15 is the largest number that can divide both 30 and 45 without leaving any remainder. Understanding the process of multiplying factors is essential for solving various mathematical problems, not only in finding the GCF but also in operations involving fractions, algebraic expressions, and more.