Tuesday, September 11, 2007

Least Common Multiple Lesson

Many people confuse least common multiples with greatest common factors. Like I told you in class today, I want you all to underline multiple when you see it and put "multiplication" right by it so that you know that you have to list the multiples of a given number.

What is a least common multiple?

The least common multiple of two or more non-zero whole numbers is actually the smallest whole number that is divisible by each of the numbers.

How to find the least common multiple?

Simply list the multiples of each number (multiply by 2, 3, 4, etc.) then look for the smallest number that appears in each list.

Example: Find the least common multiple for 5, 6, and 15.
  • First we list the multiples of each number.

Multiples of 5 are 10, 15, 20, 25, 30, 35, 40,...

Multiples of 6 are 12, 18, 24, 30, 36, 42, 48,...

Multiples of 15 are 30, 45, 60, 75, 90,....

  • Now, when you look at the list of multiples, you can see that 30 is the smallest number that appears in each list.
  • Therefore, the least common multiple of 5, 6 and 15 is 30.