Exploring the Ladder Method for LCM

The video tutorial explains prime numbers, highlighting that a prime number has only two factors: 1 and itself. It provides examples of prime numbers and notes that 2 is the only even prime number. The tutorial then introduces the concept of the least common multiple (LCM) and explains how to find it using the ladder method. This method involves writing numbers in a row, drawing an L shape, and dividing out common prime factors until no common factors remain. The LCM is found by multiplying the numbers on the outside of the L shape. An example calculation is provided to demonstrate the process.

What is a prime number?

• A number divisible by 1 and itself only

• A number divisible by 2 and 3

• A number divisible by any number

• A number that is even

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CCSS.4.OA.B.4

Which of the following is a prime number?

• 4

• 6

• 7

• 8

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CCSS.4.OA.B.4

Why is 4 not considered a prime number?

• It is greater than 3

• It is divisible by 2

• It is an even number

• It is divisible by 1 and itself

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CCSS.4.OA.B.4

What is the least common multiple (LCM)?

• The largest common multiple of a set of numbers

• The difference between the largest and smallest numbers

• The sum of a set of numbers

• The smallest common multiple of a set of numbers

What method is used to find the LCM in the video?

• Addition method

• Division method

• Subtraction method

• Ladder method

What is the first step in the ladder method?

• Write the numbers in a column

• Write the numbers in a row

• Draw a circle around the numbers

• Add the numbers together

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CCSS.1.OA.A.1

What is the smallest prime factor used in the example with 24 and 36?

• 7

• 3

• 5

• 2

What is the LCM of 24 and 36 as found in the video?

• 72

• 84

• 48

• 60

In the second example, what is the smallest prime factor used?

• 5

• 7

• 3

• 2

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CCSS.5.NBT.B.6

CCSS.6.NS.B.2

What is the LCM found in the second example?

• 54

• 72

• 24

• 36