Finding GCF and LCM with the Cake Method

This video tutorial explains how to find the Greatest Common Factor (GCF) and the Least Common Multiple (LCM) using prime factorization. It begins with an introduction to the concepts and then provides a detailed example of finding the GCF and LCM of the numbers 24 and 40. The tutorial continues with another example involving the numbers 12, 18, and 20, demonstrating the step-by-step process of using prime factors to determine both the GCF and LCM. The video emphasizes the importance of identifying the smallest prime numbers that divide the given numbers and using these to calculate the desired results.

What is the first step in finding the GCF and LCM using prime factors?

• Divide by the smallest prime number.

• Subtract the smallest number from the largest.

• Divide by the largest prime number.

• Multiply all the numbers together.

Which prime number is used first to divide both 24 and 40?

• 2

• 5

• 7

• 3

How many times does 2 go into 24?

• 10 times

• 8 times

• 6 times

• 12 times

What is the GCF of 24 and 40?

• 10

• 6

• 4

• 8

To find the LCM, what do you do with all the prime factors?

• Subtract them.

• Divide them.

• Add them together.

• Multiply them.

What is the LCM of 24 and 40?

• 180

• 240

• 320

• 120

What is the smallest prime number that goes into 12, 18, and 20?

• 3

• 5

• 7

• 2

How many times does 2 go into 18?

• 6 times

• 8 times

• 9 times

• 10 times

What is the GCF of 12, 18, and 20?

• 2

• 3

• 5

• 4

What is the LCM of 12, 18, and 20?

• 120

• 240

• 180

• 360