Problem: The number of solutions to where X is a subset of is
Answer Choices:
A.
B.
C.
D.
E. None of these
Solution:
The union of with each of the distinct subsets of results in a different solution and there are no other solutions.
Remark: In making the count, one need only enumerate the subsets of but it is not difficult to write down all solutions. This is left to the student.