Lowest Common Multiple (LCM) Explained for Students

The concept of lowest common multiple (LCM) is essential in mathematics and helps in solving real-world and exam-level problems efficiently.

Understanding Lowest Common Multiple

A lowest common multiple is the smallest positive integer that is a multiple of two or more numbers. This concept is widely used in fractions, ratios, and finding common denominators for arithmetic operations. Understanding the lowest common multiple is crucial for problem solving in maths, as well as for exams where questions on LCM, HCF, and related topics regularly appear.

How to Find the Lowest Common Multiple

There are several simple methods to calculate the lowest common multiple for any set of numbers. The three most popular techniques are:

1. Listing Multiples:
Write out several multiples of each number and identify the first (smallest) number common to all lists.

2. Prime Factorization:
Express each number as a product of prime factors. Multiply each distinct prime by the greatest number of times it occurs in any of the numbers.

3. Division Method:
Divide the numbers successively by prime numbers, recording the divisors. The product of these divisors is the LCM.

Let’s learn these methods step by step with clear examples below.

Formula Used in Lowest Common Multiple

The standard formula for the lowest common multiple of two numbers a and b is:
\( \text{LCM}(a, b) = \frac{|a \times b|}{\text{HCF}(a, b)} \)
This shows the useful relationship between LCM and HCF (highest common factor).

Here’s a helpful table to understand the lowest common multiple more clearly:

Lowest Common Multiple Table

Number Pair	Multiples	Lowest Common Multiple
4 and 6	4, 8, 12, 16, 20, 24... 6, 12, 18, 24, 30, 36...	12
6 and 8	6, 12, 18, 24, 30, 36... 8, 16, 24, 32, 40, 48...	24
8 and 12	8, 16, 24, 32, 40... 12, 24, 36, 48...	24

This table shows how finding the lowest common multiple reveals the smallest shared multiple between given numbers—useful for fractions and various calculations.

Worked Example – Solving a Problem

Example: Find the lowest common multiple of 6 and 8.

Step 1. List the first few multiples:

Step 2. Find the smallest number common to both lists:

Answer: The lowest common multiple of 6 and 8 is 24.

Alternatively, by Prime Factorization:
Step 1. Write prime factors:

Step 2. Gather all primes, using the highest power for each:

Step-by-Step Example using Division Method

Find the lowest common multiple of 12, 16, and 24.

Step 1. Arrange numbers: 12, 16, 24

Step 2. Divide by the smallest prime (2):
12 ÷ 2 = 6
16 ÷ 2 = 8
24 ÷ 2 = 12
So, write row 1: 6, 8, 12 (record “2” as divisor)

Step 3. Continue dividing any numbers still even by 2:
6 ÷ 2 = 3
8 ÷ 2 = 4
12 ÷ 2 = 6
Write row 2: 3, 4, 6 (add another “2” to divisor list)

Step 4. Again by 2:
3 (not divisible by 2) stays as 3
4 ÷ 2 = 2
6 ÷ 2 = 3
Row 3: 3, 2, 3 (record “2” again)

Step 5. Divide by 2 again:
3 stays
2 ÷ 2 = 1
3 stays
Row 4: 3, 1, 3 (add “2”)

Step 6. Now try 3:
3 ÷ 3 = 1
1 stays
3 ÷ 3 = 1
Final row is 1, 1, 1.

Multiply all divisors used: 2 × 2 × 2 × 2 × 3 = 48
So, the lowest common multiple of 12, 16, and 24 is 48.

Practice Problems

• Find the lowest common multiple of 5 and 7.
• Calculate the LCM of 9 and 12.
• List the lowest common multiple of 3, 4, and 6.
• What is the lowest common multiple of 8 and 10?

Common Mistakes to Avoid

• Confusing lowest common multiple with highest common factor (HCF).
• Stopping at the first common multiple instead of the smallest one.
• Missing prime factors or not using the highest power in prime factorization.
• Overlooking the fact that the LCM of co-prime numbers is simply their product.

Real-World Applications

The concept of lowest common multiple is vital for working with fractions—especially when adding or subtracting unlike fractions where a common denominator is needed. It is also used in tasks such as synchronising events, arranging schedules, or finding smallest groupings in packaging and distribution problems in real life. Vedantu teaches LCM concepts so students connect maths with practical thinking.

We explored the idea of lowest common multiple, how to calculate it in different ways, solved examples, common pitfalls, practice problems, and its daily life uses. Practice LCM questions and worksheets with Vedantu to build speed and confidence for your exams.

Where to Learn More

• Highest Common Factor (HCF) for understanding the link and difference between LCM and HCF.
• Multiples builds your basics before mastering LCM.
• Factors and Multiples helps to apply factor-based methods in finding LCM.
• Prime Factorization for stepwise solving with primes.
• LCM by Long Division Method for speedier solutions in exams.
• LCM by Prime Factorization to do LCM with advanced techniques.
• Application of LCM and HCF for real-world examples and practice.
• Fractions for LCM-based problems in addition/subtraction.
• Division explains how common multiples fit with division.
• Worksheet on Multiples helps practice the foundation for LCM calculation.
• Number Systems gives big picture context for LCM and its role in arithmetic.