LCM stands for "Least Common Multiple". To do this, you need to list the first few multiples of 2 or more numbers and find the common multiple(s) (common multiples [CM's] are multiples that BOTH or ALL the numbers have). For example: Find the least common multiple of 5 and 7.

To do this, list a few multiples of both 5 and 7, and see if you have any common multiples.

The common multiples of both 5 and 7 are underlined. Now, order the common multiples from least to greatest, then choose the LEAST common multiple of them all.