Final answer:
The complement of set A, denoted A', contains all elements that are not in set A. In this case, A=U, so A' will have the same number of elements as U, which is 19.
Step-by-step explanation:
The complement of set A, denoted A', consists of all elements in the sample space, S, that do not belong to set A. In this case, since A=U (universal set), A' will contain all elements that are not in the universal set. Therefore, the number of elements in A' is the same as the number of elements in the universal set. Based on the information given, the universal set has 19 elements, so A' also has 19 elements.