GCF Test #1

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In this section, we learn how to find the GCF (Greatest Common Factor) for a group of numbers. The GCF is also known as the GCD (Greatest Common Divisor). This is a common source of
confusion. If someone asks you to find the GCF or GCD for a group of numbers, they are asking for the same thing. The GCF is the largest whole number that each number in a group is divisible
by. This means we could take each number in the group and divide by the GCF and there would be no remainder. How do we find the GCF?

Greatest Common Factor:

• 20 = 2 x 2 x 5

• 50 = 2 x 5 x 5

• Common: 2, 5

• Multiply: 2 x 5 = 10

GCF of 20 and 50 is 10

Greatest Common Factor:

- Find the prime factorization of each number
- Create a list of prime factors that are common to all numbers
- The GCD is the product of the numbers on the list

• 20 = 2 x 2 x 5

• 50 = 2 x 5 x 5

• Common: 2, 5

• Multiply: 2 x 5 = 10

GCF of 20 and 50 is 10

GCF Resources:

Videos:

Khan Academy - Video
Virtual Nerd - Video
Learn Zillion - YouTube - Video
Text Lessons:

Math is Fun - Text Lesson
Math Planet - Text Lesson
Purple Math - Text Lesson
Worksheets:

Home School Math - Worksheet
K5 Learning - Worksheet
Khan Academy - Practice
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