LCM (Least Common Multiple) for Grade 4
This is a comprehensive lesson plan for teaching LCM or Least Common Multiple to grade 4 students. The lesson is designed to make the concepts easy and engage students with activities like quizzes, practice questions and worksheets.
Teachers can use this guide as a reference for delivering the concepts to students and engaging them in the classroom with the various questions and examples given on this page.
For parents, there are 12 downloadable practice worksheets that they can use for their kids.
In this blog, you will learn
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LCM - it's definition and how to find it with examples
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LCM by prime factorization method with examples
- LCM by division method with examples
What is LCM?
LCM means Least Common Multiple. It is the smallest number that happens to be a common multiple of two or more numbers.
How to find LCM?
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Write the multiples of the numbers.
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Find the common multiples.
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Choose the least common multiple.
Example 1: Find the LCM of 4 and 5
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Multiples of 4: 4, 8, 12, 16, 20, 24, 28…
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Multiples of 5: 5, 10, 15, 20, 25, 30…
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The smallest common multiple is 20. Hence LCM(4, 5) = 20.
Example 2: Determine the LCM of 6 and 8
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Multiples of 6: 6, 12, 18, 24, 30, 36…
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Multiples of 8: 8, 16, 24, 32, 40…
The smallest or least common multiple is 24. Therefore, LCM(6, 8) = 24.
LCM of 2, 3 and 4:
Multiples of 2: 2, 4, 6, 8, 10, 12, 14...
Multiples of 3: 3, 6, 9, 12, 15...
Multiples of 4: 4, 8, 12, 16...
The smallest or least common multiple is 12. Therefore, LCM(2, 3, 4) = 12.
LCM of 4 and 5:
Multiples of 4: 4, 8, 12, 16, 20...
Multiples of 5: 5, 10, 15, 20...
The smallest or least common multiple is 20. Therefore, LCM(4, 5) = 20.
LCM of 4 and 6:
Multiples of 4: 4, 8, 12, 16, 20...
Multiples of 6: 6, 12, 18, 24...
The smallest or least common multiple is 12. Therefore, LCM(4, 6) = 12.
LCM by Prime Factorization method
Prime factorization is breaking a number into prime factors, which are the smallest numbers that multiply to give the original number.
Example: Find the LCM of 12 and 15 by using the Prime Factorization method
Step 1: Prime factorization of 12: 12 = 2 × 2 × 3
Step 2: Prime factorization of 15: 15 = 3 × 5
Take all the prime factors, using the highest powers of each factor: 2, 2, 3, 5
Multiply the factors:
LCM = 2 x 2 x 3 x 5 = 60
LCM by Division Method
This method involves dividing the numbers by their common factors until no common factors are left.
Example: Find the LCM of 8 and 12 using the Division Method
Step 1: Divide by 2 (smallest prime number):
8 ÷ 2 = 4, 12 ÷ 2 = 6
New numbers: 4, 6
Step 2: Divide by 2 again:
4 ÷ 2 = 2, 6 ÷ 2 = 3
New numbers: 2, 3
Step 3: Divide again by 2 for 2 :
2 ÷ 2 = 1, 3 ÷ 2 doesn't work; divide now by 3 :
3 ÷ 3 = 1
New numbers: 1, 1
Multiply the factors: LCM = 2 × 2 × 2 × 3 × 1 = 24
Fun Fact
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Did you know that the LCM can help you when you are scheduling events?
For example, if two events happen at different times (like one every 4 days and another every 6 days), the LCM will tell you when both events will happen on the same day again. So, the LCM of 4 and 6 is 12, which means the two events will happen together every 12 days.
Quiz
1. What is the LCM of 6 and 9?
a) 18
b) 36
c) 54
d) 72
2. Find the LCM of 4 and 5.
a) 20
b) 40
c) 25
d) 10
3. What is the LCM of 8 and 12?
a) 24
b) 48
c) 36
d) 72
4. The LCM of two numbers is 60. One of the numbers is 12. What is the other number?
a) 24
b) 18
c) 15
d) 30
5. Which of the following pairs of numbers has an LCM of 18?
a) 3 and 6
b) 4 and 6
c) 2 and 9
d) 5 and 7
Orchids' learning material
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FAQs
1. How do you calculate LCM?
To calculate the LCM, list the multiples of the numbers, then find the smallest common multiple, or use prime factorization or the division method.
2. What is the LCM of 8 and 12?
The LCM of 8 and 12 is 24, as it is the smallest multiple both numbers share.
3. How to find LCM quickly?
You can find the LCM quickly by listing the multiples of each number and identifying the smallest common one or by using the prime factorization method.
4. What is the LCM rule?
The LCM rule states that the least common multiple is the smallest number, which is a multiple of each number in a given set.
Things you have learned!
- What is LCM?
- How to find LCM using the Prime Factorization Method and Division Method.