There are several methods for finding the LCM of two numbers, but the easiest for three or more is to use the factor tree method. For example, to find the LCM 9, 6, 21, and 14, use a factor tree for each number as shown.
9 6 21 14
3 3 2 3 3 7 2 7
Try to make sure your factors are in order from least to greatest. If any of the numbers have a common prime factor, write it
once and cross it off those numbers once. Write it down.
9 6 21 14
3 3
2 3 3 7
2 7
I am using a tablet, so I put my common factors in orange.
Write them down: 2
Continue to do this (next you would cross out three 3's, under the 9, 6, and 21) until no numbers have common factors. You should be left with a
3 under the 9, and a list of these common prime factors: 2, 3, 7. Write the remaining factors in your list once each. Multiply your numbers together, and you have the smallest number that can be evenly divided by each of your given numbers.
Answer: 2 x 3 x 7 x 3 = 126 (Check it out: 2 x 7 = 14, 3 x 3 = 9, and 14 x 9 = 126, so it can be divided by 14. You can check the other numbers, too.
2/22/2014

Barbara B.