Ask a question

What are 3 common multiples of 7 and 21?

Idk I just needed to ask the question I don't even know what this means

2 Answers by Expert Tutors

Tutors, sign in to answer this question.
Robert B. | Experienced (15+ years), Patient, Effective.Experienced (15+ years), Patient, Effect...
4.9 4.9 (302 lesson ratings) (302)

The "multiples" of a number, N, are the numbers N, 2*N, 3*N, ..., etc.  For example, the multiples of 4 are listed below in the usual order.

4, 8, 12, 16, 20, ..., and so on.

So by "common multiple" one means a number that is a multiple of 2 or more numbers.

Try listing the multiples of 7 and 21, separately.

You will find many numbers that appear in both lists.  These are the common multiples of 7 and 21.

In fact, you will find that every multiple of 21 is also a multiple of 7.  Do you see why?

Hope this helps.  If not, I or another tutor will be glad to further assist you.


Robert J. | Certified High School AP Calculus and Physics TeacherCertified High School AP Calculus and Ph...
4.6 4.6 (13 lesson ratings) (13)

LCM(7, 21) = 21, since 21 is a multiple of 7.

So, the three common multiples can be 1*21, 2*21 and 3*21.