That is, B is contained fully in A.
Thus, A U B = A.
Thus, |A U B|=|A|=r.
When all elements are distincy, that is A and B are disjoint.(b) What is the maximum value of |A U B|?
Then |A U B| = |A|+|B| - |A (intersect) B| =|A|+|B| *
When A and B are disjoint.(c) What is the minimum value of |A intersect B|?
That is A intersect B = empty.
Thus, |A intersect B| = 0.
When B is fully contained in A.(d) What is the maximum value of |A intersect B|?
Then, A intersect B = B
|A intersect B|=s.