• # question_answer Sets A and B have 3 and 6 elements respectively. What can be the minimum number of elements in A U B [MNR 1987; Karnataka CET 1996] A) 3B) 6C) 9D) 18

n(A È B) = n + n - n(A Ç B) = $3+6-n(A\cap B)$ Since, maximum number of elements in $A\cap B=3$ $\therefore$ Minimum number of elements in $A\cup B=9-3=6$.