Question

Set $A$and $B$ have $3$ and $6$ elements respectively. What can be the minimum number of element in $A\cup B$

• A. $3$
• B. $6$
• C. $9$
• D. $18$

Answer 1

The correct option is B $6$

$n\left(A\right)=3n\left(B\right)=6$

Minimum value of $n(A\cup B)=max\left\{n\right(A),n(B\left)\right\}=6$

This happens when A is subset of B