Basic Algebra and Geometry Made a Bit Easier Lesson Plans:
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Lesson 63: Least Common Multiples
In this easy lesson, you'll learn an important concept about multiples which is used again and again.
First, review the previous lessons on multiples of a number. To find multiples of a number, you just count by that number. For example, 3, 6, 9, 12, 15, etc. are all multiples of 3. Very often in math, there is the need to find a common multiple which is shared by two numbers. For example let's list multiples of 2: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, etc. Now let's list multiples of 5: 5, 10, 15, 20, etc. 2 and 5 have many multiples in common, for example, 10 and 20. If we kept the lists going, we would find many more. What we are usually interested in is the least common multiple (LCM). We want to know which of the common multiples is is smallest. In this example it is 10.
Here is another example. What is the LCM of 3 and 7? Multiples of 3 are: 3, 6, 9, 12, 15, 18, 21. Multiples of 7 are: 7, 14, 21. The answer is 21. It is the lowest common multiple of the two numbers.
Later you will have much more practice with this topic. For now, just make sure that you understand the general concept, and feel comfortable listing multiples of any number.
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