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LCM

How To Find LCM of 8 and 20 using Listing, Division, Prime Factorization Method?

Written by Prerit Jain

Updated on: 12 Aug 2023

How To Find LCM of 8 and 20 using Listing, Division, Prime Factorization Method?

How To Find LCM of 8 and 20 using Listing, Division, Prime Factorization Method?

LCM of 8 and 20 is 40. LCM of 8 and 20, also known as Least Common Multiple or Lowest Common Multiple of 8 and 20 is the lowest possible common number that is divisible by 8 and 20.

Now, let’s see how to find the LCM of 8 and 20. Multiples of 8 are 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88,… and multiples of 20 are 20, 40, 60, 80, 100, 120, 140, 160, 180,… Here, both 40 and 80 are the common numbers in the multiples of 8 and 20, respectively, or are divisible by 8 and 20. But, when you have to find the LCM, you must focus on the lowest common number. So, 40 is the lowest common number among all the multiples that is divisible by 8 and 20, and hence the LCM of 8 and 20 is 40.

Methods to find the LCM of 8 and 20

There are three different methods for finding the LCM of 8 and 20. They are:

  • Listing Method 
  • Division Method     
  • Prime Factorization Method

LCM of 8 and 20 Using the Listing Method

The listing method is one of the methods for finding the LCM. To find the LCM of 8 and 20 using the listing method, follow the following steps:

  • Step 1: Write down the first few multiples of 8 and 20 separately.
  • Step 2: Out of all the multiples of 8 and 20 focus on the multiples that are common to both the numbers, that is, 8 and 20.
  • Step 3: Now, out of all the common multiples, take out the smallest common multiple. That will be the LCM of 8 and 20.

LCM of 8 and 20 can be obtained using the listing method:

  • Multiples of 8 are 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88,…
  • Multiples of 20 are 20, 40, 60, 80, 100, 120, 140, 160, 180,…
  • Here, it is clear that the least common multiple is 40. So, the LCM of 8 and 20 is 40.

LCM of 8 and 20 Using the Division Method

The division method is one of the methods for finding the LCM. To find the LCM of 8 and 20 using the division method, divide 8 and 20 by the smallest prime number, which is divisible by any of them. Then, the prime factors further obtained will be used to calculate the final LCM of 8 and 20.

Follow the following steps to find the LCM of 8 and 20 using the division method:

  • Step 1: Write the numbers for which you have to find the LCM, that is 8 and 20 in this case, separated by commas.
  • Step 2: Now, find the smallest prime number which is divisible by either 8 or 20.
  • Step 3: If any of the numbers among 8 and 20 is not divisible by the respective prime number, write that number in the next row just below it and proceed further.
  • Step 4: Continue dividing the numbers obtained after each step by the prime numbers, until you get the result as 1 in the entire row.
  • Step 5: Now, multiply all the prime numbers and the final result will be the LCM of 8 and 20.

LCM of 8 and 20 can be obtained using the division method:

Prime FactorsFirst NumberSecond Number
2820
2410
225
515
 11

So, the LCM of 8 and 20 = 2 * 2 * 2 * 5 = 40

LCM of 8 and 20 Using the Prime Factorization Method

The prime factorization method is one of the methods for finding the LCM. To find the LCM of 8 and 20 using the prime factorization method, follow the following steps:

  • Step 1: Find the prime factors of 8 and 20 using the repeated division method.
  • Step 2: Write all the prime factors in their exponent forms. Then multiply the prime factors having the highest power.
  • Step 3: The final result after multiplication will be the LCM of 8 and 20.

LCM of 8 and 20 can be obtained using the prime factorization method as:

  • Prime factorization of 8 can be expressed as 2 * 2 * 2 = 21 * 21 * 21 = 23
  • Prime factorization of 20 can be expressed as 2 * 2 * 5 = 21 * 21 * 51 = 2* 51
  • So, the LCM of 8 and 20 = 2* 51= 2 * 2 * 2 * 5 = 40

What Is the Formula for Finding the LCM of 8 and 20?

LCM of 8 and 20 can be calculated using the formula:
LCM (8, 20) = (8 * 20) / HCF (8, 20),
where HCF is the highest common factor or the greatest common divisor of 8 and 20.

Another formula, using which the LCM of 8 and 20 can be found:
8 * 20 = LCM (8, 20) * HCF (8, 20), that is,
the product of 8 and 20 is equal to the product of its LCM and HCF.

Problems Based on LCM of 8 and 20

Question 1: Find the LCM of 8 and 20 using the prime factorization method.
Solution:
To find the LCM of 8 and 20 using the prime factorization method, first, we will find the prime factors of 8 and 20 using the repeated division method. Then, we will write all the prime factors in their exponent forms and multiply the prime factors having the highest power. The final result after multiplication will be the LCM of 8 and 20.

  • Prime factorization of 8 can be expressed as 2 * 2 * 2 = 21 * 21 * 21 = 23
  • Prime factorization of 20 can be expressed as 2 * 2 * 5 = 21 * 21 * 51 = 2* 51
  • So, the LCM of 8 and 20 = 2* 51= 2 * 2 * 2 * 5 = 40

 

Question 2: What is the LCM of 4, 8, and 20?
Solution:
We will find the LCM of 4, 8, and 20 using the listing method:
To find the LCM of 4, 8, and 20 using the listing method, first, we will write down the first few multiples of 4, 8, and 20 separately. Out of all the multiples of 4, 8, and 20, we will focus on the multiples which are common to all numbers.
Then, out of all the common multiples, we will take out the smallest common multiple. That will be the LCM of 4, 8, and 20.

  • Multiples of 4 are 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48,…
  • Multiples of 8 are 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88,…
  • Multiples of 20 are 20, 40, 60, 80, 100, 120, 140, 160, 180,…
  • Here, it is clear that the least common multiple is 40. So, the LCM of 4, 8, and 20 is 40.

 

Question 3: What is the least possible number which is divisible by 8 and 20?
Solution:
There are three methods using which you can find the least possible number which is divisible by 8 and 20. We will find the LCM of 8 and 20 using the division method.

  • Step 1: First, we will find the smallest prime number which is divisible by either 8 or 20.
  • Step 2: If any of the numbers among 8 and 20 is not divisible by the respective prime number, we will write that number in the next row just below it and proceed further.
  • Step 3: We will continue dividing the numbers obtained after each step by the prime numbers until we get the result as 1 in the entire row.
  • Step 4: We will multiply all the prime numbers and the final result will be the LCM of 8 and 20.
Prime FactorsFirst NumberSecond Number
2820
2410
225
515
 11

So, the LCM of 8 and 20 = 2 * 2 * 2 * 5 = 40

 

Question 4: If the LCM of two numbers is 40, HCF is 4, and one of the numbers is 20, find the other number.
Solution:
As we know,
the product of two numbers = LCM * HCF

It is given that,
one of the numbers = 20, LCM = 40, and HCF = 4

Let the other number be x.
So, 20 * x = 40 * 4
x = (40 * 4) / 20
x = 160 / 20
x = 8
Hence, the other number is 8.

 

Question 5: Find the LCM of 8 and 20 using the listing method.
Solution:
To find the LCM of 8 and 20 using the listing method, first, we will write down the first few multiples of 8 and 20 separately. Out of all the multiples of 8 and 20, we will focus on the multiples which are common to both numbers.
Then, out of all the common multiples, we will take out the smallest common multiple. That will be the LCM of 8 and 20.

  • Multiples of 8 are 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88,…
  • Multiples of 20 are 20, 40, 60, 80, 100, 120, 140, 160, 180,…
  • Here, it is clear that the least common multiple is 40. So, the LCM of 8 and 20 is 40.

Frequently Asked Questions (FAQs)

Is 80 also considered as the LCM of 8 and 20?
No, 80 is not considered as the LCM of 8 and 20. 80 is a common multiple of 8 and 20. But, it is not the least common number which is divisible by 8 and 20, and while finding the LCM, you must focus on the lowest common number. So, 40 is the lowest common number divisible by 8 and 20.

 

Are the LCM of 8 and 20 the same as the LCM of 4, 8, and 20?
LCM of 8 and 20 is 40 and LCM of 4, 8, and 20 is also 40. So, the LCM of 8 and 20 are the same as the LCM of 4, 8, and 20.

 

What is the LCM of 8 and 20?
LCM of 8 and 20 is 40.

 

Are LCM and HCF of 8 and 20 the same?
LCM of 8 and 20 is 40 and HCF of 8 and 20 is 4. So, LCM and HCF of 8 and 20 are not the same.

 

What are the methods to find the LCM of 8 and 20?
There are a total of 3 methods for finding the LCM of 8 and 20:

  • Listing Method  
  • Division Method 
  • Prime Factorization Method

We hope you understand all the basics on how to find the LCM of 8 and 20.

Written by

Prerit Jain

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