Introduction
When we need to find the smallest number that is a multiple of two or more numbers, we look for the Least Common Multiple (LCM). This is helpful in many reallife situations, such as adding fractions or planning events. Let's explore how to find the LCM of 8 and 20.
What Is LCM?
The LCM of two numbers is the smallest number that can be divided evenly by both numbers. In other words, it's the smallest number that both original numbers can "fit into." For 8 and 20, the LCM is the smallest number that both 8 and 20 can go into without leaving a remainder.
Ways To Calculate The LCM Of 8 And 20
There are several ways to calculate the LCM of 8 and 20. They include:
 Division Method
 Listing Method
 Prime Factorization Method
Prime Factorization Method
The Prime Factorization Method involves breaking down each number into its prime factors. Here’s how you can do it:
 Find the prime factors of each number.
 Write down each prime factor the greatest number of times it occurs in any single factorization.
 Multiply these prime factors together to get the LCM.
For 8:
 The prime factorization is 2 x 2 x 2, or 2³.
For 20:
 The prime factorization is 2 x 2 x 5, or 2² x 5¹.
To find the LCM, take the highest powers of all prime numbers present:
 LCM = 2³ x 5¹ = 8 x 5 = 40.
So, the LCM of 8 and 20 using the Prime Factorization Method is 40.
Division Method
The Division Method divides the numbers by their common prime factors until we are left with only 1s. Here’s how it works:
 Write 8 and 20 next to each other.
 Divide both numbers by the smallest prime number that can divide either of them.
 Keep dividing the results until all results are 1.
Let's see this for 8 and 20:

8 and 20 are divided by 2 (the smallest prime number):
 8 / 2 = 4
 20 / 2 = 10

Next, we continue dividing by 2:
 4 / 2 = 2
 10 / 2 = 5

Continue dividing by 2:
 2 / 2 = 1
 5 / 2 = 5 (since 5 is not divisible by 2, it remains 5)
 Finally, divide by 5:
 1 / 5 = 1
 5 / 5 = 1
The LCM is then the product of all these prime numbers:
 2 x 2 x 2 x 5 = 40
So, the LCM of 8 and 20 using the Division Method is 40.
Listing Method
The Listing Method involves listing the multiples of each number until we find the smallest common multiple. Here’s how:
 List multiples of each number.
 Identify the smallest number that appears in both lists.
For 8:
 Multiples: 8, 16, 24, 32, 40, 48, …
For 20:
 Multiples: 20, 40, 60, 80, 100, …
The smallest common multiple in both lists is 40.
So, the LCM of 8 and 20 using the Listing Method is 40.
Formula For Calculating LCM
The general formula to find the LCM of two numbers using their Greatest Common Divisor (GCD) is:
LCM (a, b) = (a x b) / GCD (a, b)
For 8 and 20:
 The GCD of 8 and 20 is 4 (calculated using the Euclidean algorithm).
Hence,
LCM (8, 20) = (8 x 20) / 4 = 160 / 4 = 40
Conclusion
We have explored different ways to find the Least Common Multiple of 8 and 20. By understanding and using methods like Prime Factorization, Division, or Listing, we can easily calculate the LCM. In all cases above, the LCM of 8 and 20 is 40.
FAQs
What is the LCM of 8 and 20?
 The LCM of 8 and 20 is 40.
Why is finding the LCM important?
 Finding the LCM is useful for solving problems in arithmetic involving fractions, ratios, and reallife scenarios that require synchronization of events or cycles.
Is there a fastest method to find the LCM?
 The fastest method might vary depending on the numbers involved. Prime Factorization is often efficient for smaller numbers, while the formula involving GCD can be quicker for larger numbers.