What Is the Lowest Common Multiple? An Easy Guide for Elementary Students
Understanding the lowest common multiple (LCM) helps students work with fractions that have different denominators. Most children are introduced to this concept in 5th grade, when they start learning how to rewrite fractions with common denominators and solve problems involving uneven groups. In this blog, we’ll explain what the lowest common multiple is and how to make it easier for elementary students to grasp. And if your child could use extra support, an elementary math tutor can help reinforce these skills with one-on-one guidance.
What is the lowest common multiple?
The lowest common multiple (LCM) is the smallest number that two or more numbers have in common when listing their multiples. For example, the common multiples of 4 and 6 include 12 and 36. Since 12 is the smallest, it’s the lowest common multiple of 4 and 6.
How to find the lowest common multiple
LCM using the listing method
This is a simple way to find the lowest common multiple, especially when working with smaller numbers. Here’s how to do it:
- Write down the first few multiples of both numbers.
- Find numbers that appear in both lists.
- Choose the smallest number on both lists. That’s the LCM.
This method works well for helping students understand the concept visually and through repetition.
LCM using the prime factorization method
This method breaks numbers down into their basic building blocks—prime factors—and uses those to find the LCM. Here’s how:
- Use repeated division to find the prime factors of every number.
- Write those prime factors in exponent form.
- Multiply together the prime factors using the highest power of each. The result is the LCM.
This approach is helpful when working with larger numbers, and it reinforces important concepts about factors and multiplication.
LCM using the division method
The division method is a step-by-step process that uses prime numbers to simplify and solve. Follow these steps:
- Choose a prime number that divides at least one of the given numbers. Write it on the left side of the numbers.
- If the prime number divides evenly into a number, divide and write the result below. If not, keep the number as is.
- Continue dividing until all the numbers reach 1. Multiply all the prime numbers on the left to get the LCM.
This technique organizes the work and helps students build confidence using division and multiplication together.
Our math tutors can help
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