Answer
84
Work Step by Step
The least common multiple (LCM) of a group of numbers is the smallest number that is divisible by all of the numbers in the group. In order to find the LCM of 4, 12, and 21, we can find the smallest multiple of 21 that is divisible by both 4 and 12.
21- not divisible by either
42- not divisible by either
63- not divisible by either
84- divisible by both
$84\div4=21$
$84\div12=7$
Therefore, the LCM of 4, 12, and 21 is 84.
