Question:
Let $A$ and $B$ be two sets such that $n(A)=5, n(B)=3$ and $n(A \cap B)=2$.
(i) $n(A \cup B)$
(ii) $n(A \times B)$
(iii) $n(A \times B) \cap(B \times A)$
Solution:
(i) $n(A \cup B)=n(A)+n(B)-n(A \cap B)$
$=5+3-2$
$=6$
(ii) $n(A \times B)=n(A) \times n(B)$
$=5 \times 3$
$=15$
(iii) $n(A \times B) \cap(B \times A)=n(A \times B)+n(B \times A)-$
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