Problem
Let \( A = \{1, 2, 3, 4\} \) and \( B = \{3, 4, 5, 6\} \). Find the cardinality of \( A \cup B \).
Solution
Step 1 ：First, we find the union of sets A and B, which is \( A \cup B = \{1, 2, 3, 4, 5, 6\} \).
Step 2 ：Then, the cardinality of a set is the number of elements in the set. Here, the number of elements in \( A \cup B \) is 6.
