Finding the LCM of Three Numbers with Prime Factorization

In this video, Mr. J explains how to find the least common multiple (LCM) of three numbers using prime factorization. He demonstrates the process with the numbers 21, 28, and 32, breaking each down into their prime factors. The video covers aligning these factors vertically and calculating the LCM by multiplying the necessary factors. This method is particularly useful for larger numbers where listing multiples is inefficient.

What is one advantage of using prime factorization to find the LCM over listing multiples?

• It is easier to understand.

• It is more efficient for larger numbers.

• It requires less mathematical knowledge.

• It is faster for smaller numbers.

What are the prime factors of 21?

• 2 and 14

• 3 and 7

• 2 and 7

• 3 and 14

Which of the following is a prime factor of 28?

• 2

• 32

• 21

• 14

Tags

CCSS.4.OA.B.4

How many times do you need to break down the number 32 to get its prime factors?

• 3 times

• 4 times

• 2 times

• 5 times

When listing the prime factors of 21, 28, and 32, which number is matched vertically first?

• 2

• 3

• 7

• None of the above

How many columns of 2s are there when matching the prime factors of 21, 28, and 32?

• 5

• 3

• 2

• 4

Tags

CCSS.4.OA.B.4

What is the next step after listing and matching the prime factors vertically?

• Adding the numbers in each column

• Dividing the numbers in each column

• Multiplying the numbers in each column

• Bringing down a number to represent each column

What is the result of multiplying 2 to the fifth power?

• 16

• 32

• 64

• 128

Tags

CCSS.6.EE.A.1

What is the product of 3 times 7?

• 28

• 21

• 14

• 10

Tags

CCSS.3.OA.C.7

What is the least common multiple (LCM) of 21, 28, and 32?

• 512

• 256

• 128

• 672