LCM is an acronym for "Least Common Multiple." LCM is the smallest number that is a multiple of two or more numbers.
List the multiples of each number. In our example, the multiples of 5, 6, and 15 are listed. Now, look at the list of multiples and find the smallest number that all of the numbers have in common. Once you find the smallest number, you have finally found the LCM! In this example, the smallest number that all of the numbers share is 30, therefore, making the LCM = 30.
Practice LCM by playing this game : http://www.fun4thebrain.com/beyondfacts/lcmsnowball.html