Question

if n (A)=4, n (B) =9, and n(A ∩ B) =2; what is n( A U B)?

Answer 1

Given:

$\begin{gathered} n(A)=4 \\ n(B)_{}=9 \\ n\mleft(A\cap B\mright)=2 \end{gathered}$

To find:

$n(A\cup B)$

Using the formula,

$\begin{gathered} n(A\cup B)=n(A)+n(B)-n(A\cap B) \\ =4+9-2_{} \\ =11 \end{gathered}$

Hence the answer is 11.