union and intersection of two sets

Question

Let  and 

Find the following:

LIST the elements in the set :

 = {  }

Enter the elements as a list, separated by commas. If the result is the empty set, enter DNELIST the elements in the set :

 = {  }

Enter the elements as a list, separated by commas. If the result is the empty set, enter DNE

Answer 1

A U B = {1,2,5,6, 7,8,12,13,15,18,20}

It's the elements of B plus 7 and 13

or the elements of A plus 5,12, 18 and 20

Just list every one of A and B's elements but if there is two of one element use only 1 of them. so use only one 1, one 2, one 6 and one 15. they all appear in both A and B

A intersection B = {1,2,6, 15}

these are the elements that are in both A and in B