Understanding LCM and GCF

This video tutorial explains how to find the least common multiple (LCM) and greatest common factor (GCF) of the numbers 20 and 30 using factor trees. It demonstrates creating factor trees for both numbers, identifying their prime factors, and then using these factors to calculate the LCM and GCF. The video concludes with a summary and a call to action for viewers to subscribe for more math and science content.

What is the purpose of using a factor tree in this video?

• To identify the prime factors of a number

• To determine the average of two numbers

• To calculate the square root of a number

• To find the sum of two numbers

Which of the following is a prime factor of 20?

• 3

• 4

• 6

• 5

What are the prime factors of 30?

• 1, 2, and 3

• 3, 5, and 7

• 2, 3, and 5

• 2, 4, and 6

How do you calculate the LCM of two numbers using their prime factors?

• Divide the larger number by the smaller number

• Multiply all the prime factors together, using common factors only once

• Add all the prime factors together

• Subtract the smaller number from the larger number

What is the LCM of 20 and 30?

• 70

• 60

• 50

• 40

What is the definition of the Greatest Common Factor (GCF)?

• The difference between the two numbers

• The largest number that divides both numbers

• The smallest number that divides both numbers

• The sum of the two numbers

Which prime numbers are common in both 20 and 30?

• 2 and 4

• 2 and 5

• 3 and 5

• 2 and 3

What is the GCF of 20 and 30?

• 10

• 5

• 15

• 20

Why is the number 3 not considered in the GCF of 20 and 30?

• It is not a prime number

• It is not a factor of 20

• It is not a factor of 30

• It is not a common factor

What is the final step in finding the GCF of two numbers?

• Dividing the larger number by the smaller number

• Subtracting the smaller number from the larger number

• Multiplying the common prime factors

• Adding the prime factors