Null sets:
The set of squares with 5 sides.
The set of cars with 20 doors.
The set of integers which are both even and odd.

Rule method:
A = {x | x  N, x > 100}
B = {x l x is the set of all colors of the rainbow}
C = {x l x is the set of all counting numbers up to 100}

2 5 2