Which of the following describes the least common multiple (LCM)?

• A. The largest number that divides both numbers.
• B. The smallest positive number that is a multiple of both numbers.
• C. The difference between the two numbers.
• D. The sum of the two numbers.

Answer: (B)

The least common multiple is the smallest positive number that is a multiple of both numbers. It’s the first time the multiples of the two numbers line up. For example, multiples of 4 are 4, 8, 12, 16… and multiples of 6 are 6, 12, 18, 24…. The first common multiple is 12, so the LCM of 4 and 6 is 12. The other descriptions refer to different ideas: the largest number that divides both numbers is the greatest common divisor, the difference is subtraction, and the sum is addition. So the correct description is the smallest positive number that is a common multiple.