Given:
[tex]\begin{gathered} n(A)=4 \\ n(B)_{}=9 \\ n\mleft(A\cap B\mright)=2 \end{gathered}[/tex]To find:
[tex]n(A\cup B)[/tex]Using the formula,
[tex]\begin{gathered} n(A\cup B)=n(A)+n(B)-n(A\cap B) \\ =4+9-2_{} \\ =11 \end{gathered}[/tex]Hence the answer is 11.
