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Last updated on May 26th, 2025

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LCM of 21 and 24

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The meaning of least common factor (LCM) is to find the smallest number that divides any two integers evenly. LCM is used mainly in fractions to find a common number for both the integers. We use LCM for solving problems, lining up cycles or even synchronizing of events, also to schedule tasks in everyday life.

LCM of 21 and 24 for UK Students
Professor Greenline from BrightChamps

What is the LCM of 21 and 24?

We use LCM of 21 and 24 to find  the smallest number that divides both the numbers equally.  The smallest positive number is the number that divides both numbers equally, is 168 without leaving any remainder. LCM is used mainly in fractions to find a common number for both the integers.
 

Professor Greenline from BrightChamps

How to find the LCM of 21 and 24?

The LCM of 21 and 24 can be found by the following methods like division method, listing multiples, prime factorization.
 

Professor Greenline from BrightChamps

LCM of 21 and 24 using Division method:

In division method, we divide both the numbers, we begin with dividing side by side the smallest number. We continue dividing until we get a common number that divides both the numbers equally. It makes it easier for the children to focus on prime factors and identify them.

 

  • 2 divides 24 and not 21

 

  • 3 divides 24 and 21

 

  • 12 divides 24 and not 21

 

  • 7 divides 21 and not 24.

 

Now multiply the divisors : 2×3×4×7=168 which is the LCM.
 

Professor Greenline from BrightChamps

LCM of 24 and 21 using Listing multiples:

Step 1: Start by listing multiples of both the numbers separately:


Multiples of 21 are 21,42,63,84,105,126,147,168…..


Multiples of 24 are 24,48,72,96120,144,168…..

 

Step 2: The least common factor from the list is 168. Therefore, the LCM of 24 and 21 is 168.

Professor Greenline from BrightChamps

LCM of 24 and 21 using Prime factorization:

We part both the numbers unto factors:


Factor of 24: 23×3


Factors of 21: 3×7

 

Take the powers of both the numbers and multiply together:


LCM=23x3x7=168.
 

Max Pointing Out Common Math Mistakes

Common Mistakes and How to Avoid Them in LCM of 24 and 21

While solving problems based on the LCM of 24 and 21, children fail to understand few concepts, to give an idea of the mistakes, given below are a few mistakes and solutions of how to avoid them:

Mistake 1

Red Cross Icon Indicating Mistakes to Avoid in This Math Topic

Stopping the division method way too soon.
 

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Students sometimes stop dividing very soon, when they are not able to divide both the numbers with the same number. For example, we can divide14 by 2, but 15 isn't divisible by 2. To continue the dividing method until all the factors are found. The students should continue dividing until they find the common number that divides both the integers.
 

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LCM of 24 and 21 Examples

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Max, the Girl Character from BrightChamps

Problem 1

Is 504 a common multiple of 24 and 21?

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504/ 24=21


504/21=24
 

Explanation

As both divisions leave no remainder, 504 is a common multiple of 24 and 21.
 

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Max, the Girl Character from BrightChamps

Problem 2

Simplify the fraction 24/21 using the GCD of the numerator and denominator.

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 the simplified fraction is 8/7.
 

Explanation

GCD (24,21) =3
Divide both numerator and denominator by 3:
24/3  ÷ 21/3=8/7
Therefore, the simplified fraction is 8/7.

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Max, the Girl Character from BrightChamps

Problem 3

List the first 5 multiples of 24 and 21. Identify the LCM from these lists.

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Multiples of 24: 24,48,72,96,120,144,168,…


Multiples of 21: 21,42,63,84,105,126,147,168,….
 

Explanation

 LCM of 24 and 21 = 168

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Max, the Girl Character from BrightChamps

Problem 4

Find the value of X, if LCM(24,X)=168.

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 Answer:    X=21.
 

Explanation

Using the formula :

 
LCM(a, b) x GCD(a, b)=a × b


LCM(24,X)=168


GCD(24,X)=unknown


As the product of numbers should be equal to 168, so X=21.


LCM(24,21)=168.


X=21.
 

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Max, the Girl Character from BrightChamps

Problem 5

Find the simplified form of 24/21.

Ray, the Boy Character from BrightChamps Saying "Let’s Begin"

GCD(24,21)=3
24/ 21 = 24÷3 / 21 ÷3  = 8/7

Explanation

 simplified form of 24/21 is 8/7

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FAQ’s on LCM of 24 and 21

1. What is the number that can be divided by 21 and 24?

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2.There are how many factors in 4800?

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3.Write the LCM of 21,24, and 18?

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4.What is the GCF of 240 and 360?

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5.What is the GCF of 300 by factor tree method?

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6.How can children in United Kingdom use numbers in everyday life to understand LCM of 21 and 24?

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7.What are some fun ways kids in United Kingdom can practice LCM of 21 and 24 with numbers?

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8.What role do numbers and LCM of 21 and 24 play in helping children in United Kingdom develop problem-solving skills?

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9.How can families in United Kingdom create number-rich environments to improve LCM of 21 and 24 skills?

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Professor Greenline from BrightChamps

Important glossaries on the LCM of 24 and 21

  • Prime Factor: A natural number or whole number which has factors that are 1 and itself. For Example, 3 is a prime number.

 

  • Prime Factorization: The process of breaking down a number into its prime factors is called Prime Factorization. For example, the factorization of 14 is 2×7.

 

  • Co-prime numbers: numbers which has the only positive divisor of them both as 1. For example, 6 and 7.
     
Professor Greenline from BrightChamps

About BrightChamps in United Kingdom

At BrightChamps, we know numbers are far more than mere digits—they open doors to endless opportunities! We aim to support children all over the United Kingdom in mastering essential math skills, with today’s spotlight on the LCM of 21 and 24 and a special focus on understanding the LCM—in a lively, enjoyable, and easy-to-understand way. Whether your child is working out how fast a roller coaster travels at Alton Towers, tracking scores at a local football match, or budgeting pocket money for the latest gadgets, mastering numbers helps build their everyday confidence. Our interactive lessons make learning fun and straightforward. Since children in the UK learn in diverse ways, we adapt our teaching to suit each individual. From the bustling streets of London to the scenic coastlines of Cornwall, BrightChamps makes math relatable and exciting throughout the UK. Let’s bring the LCM to life for every child’s math journey!
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Hiralee Lalitkumar Makwana

About the Author

Hiralee Lalitkumar Makwana has almost two years of teaching experience. She is a number ninja as she loves numbers. Her interest in numbers can be seen in the way she cracks math puzzles and hidden patterns.

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Max, the Girl Character from BrightChamps

Fun Fact

: She loves to read number jokes and games.

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