Least Common Multiple

Part of the Factors & Fractions section of Coddy's Pre-Algebra journey. Lesson 14 of 58.

A common multiple of two numbers is on both of their lists of multiples. Multiples of 4: 4, 8, 12, 16, 20, ... Multiples of 10: 10, 20, 30, ... The first number on both lists is 20, so 20 is the least common multiple, or LCM, of 4 and 10.

40, 60 and 80 are common multiples too, and the list never ends, which is why the question is about the least one. The LCM is the smallest number both go into: 20 / 4 is 5 and 20 / 10 is 2.

A quicker way: count up through the multiples of the larger number, 10, 20, 30, and stop at the first one the smaller number divides. The larger number's list climbs faster, so you reach the answer sooner. Later in this section the LCM is what lets you add fractions with different bottoms.

Challenge

Find the least common multiple L of 6 and 8. Count up through the multiples of 8 until you reach one that 6 divides, write L = ... on the board, then press Check.