Least Common Multiple – Definition, Method, Solved Examples
Welcome to another exciting exploration of a fundamental mathematical concept, brought to you by Brighterly, your trusted partner in making learning fun and engaging for children. Today, we’re diving into the world of multiples, specifically the Least Common Multiple (LCM). This concept is as intriguing as it is vital. It serves as a cornerstone in number theory and plays an instrumental role in dealing with fractions and ratios, skills necessary for a child’s academic journey.
When we talk about LCM, we’re looking at the smallest common multiple shared by two or more numbers. This concept often becomes a child’s first encounter with number relations that move beyond basic arithmetic. Let’s take an example: For the numbers 3 and 4, the multiples of 3 are 3, 6, 9, 12, 15, and so on, while those of 4 are 4, 8, 12, 16, and so on. Spot the smallest number that shows up in both lists? That’s right, it’s 12, which makes it the LCM of 3 and 4. Understanding LCM is a stepping stone towards more complex mathematical problemsolving, like dealing with fractions, proportions, and other mathematical challenges that your child will encounter in their educational journey. With Brighterly, we’ll make this journey not only insightful but also enjoyable!
What is Least Common Multiple (LCM)?
The Least Common Multiple, often abbreviated as LCM, is a fundamental concept in the mathematical realm, especially in the field of number theory and fractions. It’s a term that frequently pops up in the math syllabus of children, making it an essential concept to understand for them.
So, what is it? In the simplest terms, the Least Common Multiple of two or more numbers is the smallest number that is a multiple of all the numbers in question. For instance, consider two numbers, 4 and 5. The multiples of 4 are 4, 8, 12, 16, 20, 24, and so on, while the multiples of 5 are 5, 10, 15, 20, 25, and so on. The smallest number that appears in both lists is 20. Hence, 20 is the LCM of 4 and 5. Understanding the concept of LCM is crucial for problemsolving in mathematics, especially when dealing with fractions, ratios, and other similar topics.
Properties of LCM
The Least Common Multiple is not just a concept, it carries some unique properties that are fascinating to learn. Here are some important properties of LCM:
 For any number, the LCM of the number and 1 is the number itself. For example, the LCM of 7 and 1 is 7.
 The LCM of two numbers is always equal to or larger than both the numbers. In other words, if a and b are two numbers, then LCM(a, b) ≥ max(a, b).
 If two numbers are coprime (i.e., their greatest common divisor is 1), then the LCM of the two numbers is the product of the numbers. For example, the LCM of 3 and 5, which are coprime numbers, is 15.
 The LCM of two or more numbers is the same regardless of the order in which the numbers are arranged.
These properties not only make the concept of LCM interesting but also help in simplifying various mathematical problems and calculations.
How to Find LCM?
To find the Least Common Multiple of two or more numbers, there are various methods you can employ. These methods include the Listing the Multiples Method, the Prime Factorization Method, the Division Method, and the use of the LCM Formula. Each method has its own benefits and is used based on the complexity and size of the numbers involved. In the upcoming sections, we will delve deeper into each of these methods and learn how they are used to find the LCM.
To solidify your newfound knowledge of the Least Common Multiple and apply it to various problems, check out our engaging LCM Worksheet on Brighterly. This resource is teeming with fun and challenging exercises designed to help you further grasp this vital mathematical concept. The answers are also conveniently provided for you to review your solutions. Happy learning!
LCM Formula
In certain situations, you can use the LCM formula to find the least common multiple of two numbers. The formula is LCM(a, b) = (a * b) / GCD(a, b), where GCD stands for the Greatest Common Divisor of the numbers a and b. This formula is useful especially when the numbers involved are large, making it difficult to use other methods. But remember, to use this formula, you need to first find the GCD of the numbers.
LCM Formula for Fractions
When it comes to finding the LCM of fractions, the formula changes a bit. For two fractions, a/b and c/d, the LCM is given by LCM(a, c) / GCD(b, d). This formula is useful when dealing with problems involving fractions, such as adding, subtracting, or comparing fractions.
Listing the Multiples Method
The Listing the Multiples Method is one of the simplest ways to find the LCM of two or more numbers. It involves listing the multiples of the given numbers and then identifying the smallest multiple that is common to all the numbers. This method is best suited for smaller numbers or when the LCM is relatively small.
Prime Factorization Method
The Prime Factorization Method is another technique to find the LCM of two or more numbers. It involves breaking down the numbers into their prime factors and then multiplying the highest powers of all the prime factors involved. This method is particularly useful when dealing with larger numbers or when other methods are too timeconsuming.
Division Method
The Division Method is an alternative approach to find the LCM of two or more numbers. It involves dividing the numbers by their common divisors until no common divisor other than 1 remains. The LCM is then found by multiplying the divisors and the remaining numbers. This method can be helpful when the numbers involved have many common divisors.
Relationship Between LCM and HCF
LCM and HCF (Highest Common Factor) are closely related. As mentioned earlier, the LCM formula is LCM(a, b) = (a * b) / GCD(a, b). The relationship between LCM and HCF can be expressed as LCM(a, b) * HCF(a, b) = a * b for any two numbers a and b. This relationship is useful in various mathematical problems and calculations.
Difference Between LCM and HCF
While LCM and HCF are related, they serve different purposes in mathematics. LCM is the smallest number that is a multiple of two or more numbers, whereas HCF is the largest number that divides two or more numbers. In essence, LCM deals with multiples, while HCF deals with factors.
LCM of Two Numbers
To find the LCM of two numbers, you can use any of the methods discussed earlier, such as Listing the Multiples Method, Prime Factorization Method, Division Method, or the LCM Formula.
LCM of Three Numbers
Finding the LCM of three numbers is not much different from finding the LCM of two numbers. You can still use the methods mentioned earlier. One common approach is to first find the LCM of the first two numbers and then find the LCM of the result and the third number.
Solved Examples On Least Common Multiple
Here are some solved examples to help you understand the concept of LCM better:

Example 1: Find the LCM of 4 and 5 using the Listing the Multiples Method.
 Multiples of 4: 4, 8, 12, 16, 20, 24…
 Multiples of 5: 5, 10, 15, 20, 25…
 The smallest common multiple is 20. So, LCM(4, 5) = 20.

Example 2: Find the LCM of 6, 8, and 12 using the Prime Factorization Method.
 Prime factors of 6: 2 × 3
 Prime factors of 8: 2 × 2 × 2
 Prime factors of 12: 2 × 2 × 3
 LCM(6, 8, 12) = 2³ × 3 = 24
Practice Problems On Least Common Multiple
 Find the LCM of 15 and 20.
 Find the LCM of 9, 12, and 18.
 Find the LCM of 7, 14, and 21.
Conclusion
As we wind up this enlightening journey through the fascinating landscape of the Least Common Multiple (LCM), we are grateful you chose to embark on this mathematical adventure with Brighterly. We hope that this guide has shed light on this significant mathematical concept that is critical in elementary mathematics and beyond.
The LCM is not just about finding the smallest multiple shared by numbers. It’s about understanding mathematical relationships and patterns that will help your child solve more complex problems involving fractions, ratios, and more. It’s about equipping your child with the tools they need to excel in mathematics.
Through the exploration of the various methods of finding the LCM – Listing the Multiples Method, Prime Factorization Method, Division Method, or using the LCM formula – your child now has a toolkit they can apply depending on the numbers involved. Understanding the properties of LCM, its relationship with HCF, and the differences between the two, is more than just knowledge – it’s an arsenal for mathematical problemsolving.
As always, at Brighterly, we strive to make learning exciting and fun. We hope that this exploration of LCM has sparked a love for learning and an appreciation for the beauty of mathematics in your child. We look forward to sharing more enlightening and engaging content to further help your child excel in their academic journey. After all, at Brighterly, we believe that every child’s future can be brighter!
Frequently Asked Questions On Least Common Multiple
What is the LCM of two prime numbers?
The LCM of two prime numbers might seem like a complicated concept at first, but it’s actually quite simple when you break it down. Remember, a prime number is a number that has only two factors: 1 and the number itself. That means prime numbers do not share any other factors with other numbers. So, when you’re trying to find the LCM of two prime numbers, it’s actually just the product of the two numbers. This is because their only common multiple (other than 1) is found by multiplying the two numbers together. For example, the prime numbers 2 and 3 have an LCM of 6 (because 2*3=6), which is their product.
Can the LCM of two numbers be one of the numbers?
Yes, the LCM of two numbers can indeed be one of the numbers. This happens in a scenario where one number is a multiple of the other. In such a case, the larger number is already a multiple of the smaller one, so it naturally becomes the Least Common Multiple. For example, if we take the numbers 3 and 9, we can see that 9 is a multiple of 3. Therefore, the LCM of 3 and 9 is 9. It’s an interesting facet of the LCM that shows just how interconnected numbers can be!
Why do we need to find the LCM in fractions?
Finding the LCM plays an integral role when dealing with fractions, specifically when adding or subtracting them. Here’s why: to add or subtract fractions, you need to have a common denominator. If the denominators are different, you find their LCM and use it as the common denominator. By doing this, you’re able to add or subtract the fractions without changing their inherent value. For example, when adding 1/4 and 2/3, the LCM of 4 and 3 is 12. We adjust the fractions to have the common denominator (making them 3/12 and 8/12), and then we can easily add them to get 11/12. So, finding the LCM is a crucial step in performing operations with fractions.
Sources of Information
To create this comprehensive guide on LCM, a range of reliable sources were used, including academic websites and government educational resources. These include:
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