Question

Suppose U= {x|x is a multiple of 3, x greater than or equal to 18} is the universal set and C= {21, 24, 27,30}. What is C?

Answer 1

can you form the set U ?

Answer 2

Thats what I am stuck on turning that into roster form.

Answer 3

ok, so it just asks you to find multiples of 3 that are >=18
start with 18, which numbers are next ?

Answer 4

21, 24, 27,30,33,36,39...

Answer 5

correct!
so you have
U = {18,21,24, 27,30,33,36,39...}
and C= {21, 24, 27,30}
so you notice that all elements of C are present in U !! isn't it ?
what is C called then ? any ideas ?

Answer 6

complement I think

Answer 7

not actually, ever heard of subsets ?

Answer 8

yeah I just wasnt sure..

Answer 9

so the C is the subset of U :)

Answer 10

any more doubts on this ?