Answer: 21
Step-by-step explanation: To find the LCM or least common multiple of 3 and 7, begin by finding the first few multiples of each number and compare the lists.
The multiples of 3 that we list are as followed.
1 x 3 = 3
2 x 3 = 6
3 x 3 = 9
4 x 3 = 12
5 x 3 = 15
6 x 3 = 18
7 x 3 = 21
The multiples of 7 that we list are as followed.
1 x 7 = 7
2 x 7 = 14
3 x 7 = 21
Since 21 appears in both lists, we can stop here.
So the least common multiple of 3 and 7 is 21.