 In this video, we provide the solution to question number one for practice exam number four for math 1030 for which we're given two sets A and B, which are illustrated right here. They appear to be sets of whole numbers ranging from one up to 20, and we're asked to compute the cardinality of the union of A and B there. Now, to find the union of A and B, we put the two sets together. So we grab anything that's in A or in B, but I have to find the cardinality. So I only have to do is count the size of A union B. Now, to make sure I count this correctly, I want to look for any duplicates look for elements which are in A and B to make sure I don't count them twice. So you'll notice that A and B both contain one, two, three, seven, 12, 14, 16 and 17. Every other element is unique. A has an eight and a 10 that B doesn't but B has a five and a nine and 1920 those other elements I slashed out showed up in both sets. So then we can count how many elements are there because if you put those elements together that gives you a union B a union B is going to be the set containing 123578910121416171920. How many numbers is that? That's one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14. So the correct answer would then be E.