Least Common Multiple|Definition & Meaning

The Least Common Multiple is the meaning of the abbreviation LCM. The lowest number that may be divided by both numbers is known as the LCM of two numbers. It can also be computed using two or more numbers. Finding the LCM of any particular number can be done in a variety of ways. 

Applying the prime factorization for each number and then calculating the product of the greatest powers of the shared prime factors is one of the quickest techniques to determine the LCM of two numbers.

Figure 1 – LCM of 2 and 5

In the above figure, the common multiple of 2 and 5 are 10 and 20 but the smallest is 10 so the LCM of 2 and 5 is 10.

Methods To Find LCM

There are different methods to find LCM. Mainly there are three methods to find the LCM of any two numbers.

1. Prime Factorization Method
2. Listing Method
3. Division Method

Prime Factorization Method

The LCM of the supplied numbers can be determined by applying the prime factorization method. The following steps are used to determine the LCM by the prime factorization method:

Step 1

By using the repeated division method, determine the given numbers’ prime factors.

Step 2

The numbers should be expressed in exponentiation. Only those prime factors’ products with the highest power should be sought.

Step 3

The LCM of the provided numbers is the result of these factors’ highest powers combined.

Figure 2 – LCM of 12 and 18 by Prime Factorization Method

Listing Method

By listing the multiples of two or more numbers, we can determine the common multiples of those numbers. The LCM among these frequent multiples is taken into account, allowing the LCM of any two values to be determined. The steps below are used to determine the Least Common Multiple of the two numbers by using the listing approach.

 Step 1

Write some first multiples of two given numbers of which we must find LCM.

Step 2

Mark the common multiples of both numbers.

 Step 3

For LCM, choose the smallest multiple of both numbers. That common number will be the LCM of both numbers.

The below figure shows the LCM of 10 and 50 by the Listing Method.

Figure 3 – LCM of 10 and 50 by Listing Method

Here, the first few multiples of 10 and 50 have been written. The common multiple in both numbers is 50 and 100, but LCM means the least common multiple. We can see from Figure 3 that the smallest common multiple for 10 and 50 is just 50, so we write LCM(10, 50) = 50.

Division Method

To find the LCM using the method of division, we first write the supplied numbers in a row separated by commas. Then, we divide each of those numbers by a common prime number. As soon as we reach one of the prime numbers, we stop dividing. The least significant factor of a set of numbers is the product of its common prime factors and its uncommon prime factors.

Step 1

Create a line with the given numbers, separating them with commas.

Step 2

Divide them by an appropriate prime number, one that perfectly divides at least two of the numbers that have been provided.

Step 3

We wrote the quotient directly beneath the values in the row that followed it. In the event that the number cannot be divided exactly, the remainder is taken down in the next row.

Step 4

Step 2 and also step 3 are repeated as necessary until there are no more co-prime numbers in the bottom row.

Step 5

After that, we multiply all of the prime numbers with which we’ve divided as well as the co-prime numbers that are still in the last row. The offered numbers have the fewest possible multiples in common with this product.

Figure 4 – LCM of 12 and 18 by Division Method

The above figure shows the LCM of 12 and 18 by the division method. From the figure, we can really see that the LCM of 12 and 18 is 36.

Examples of Finding the Least Common Multiple

Example 1

Example 2

Find the LCM of 25 and 50 by listing method.

Solution

Here in this example, we will write the multiples of the given two numbers that is 25 and 50.

25 = 25, 50, 75, 100, 125, 150, 175, 200

50 = 50, 100, 150, 200, 250, 300

We can see here the common multiples are 50,100,150,200. Since the least common multiple is 50, so:

LCM(25,50) = 50

Example 3

Find the LCM of 20 and 30 by the division method.

Solution

The two numbers, 20 and 30, will be divided up to 1, and then the divisor will be multiplied to get LCM.

Figure 5 – LCM of 20 and 30 by Division Method

The two numbers are 20 and 30. First will see the lowest multiple, which is 2. Both the numbers are divisible by 2. When 20 is divided by 2, the answer is 10, which is written below 20. When 30 is divided by 2, the answer is 15, which is written below 30.

Now, 10 and 15 are divided by the number. Here 10 is divisible by 2, but 15 is not divisible by 2, so we will divide just 10, so the answer is 5, which will be written below 10, and 15 will be written as it is.

Now we got 5 and 15, which are divisible by 5. When 5 is divided by 5, the answer is 1, which is written below 5. When 15 is divided by 5, the answer is 3, which is written below 15.

In the end, only 3 is left, which will be divided by 3. When we multiply the prime numbers, we will get LCM. The LCM of 20 and 30 is 60. It will be written as LCM(20, 30) = 60.

All the figures above are created on GeoGebra.

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