Question

questions about SETS ??? and counting?

Answer 1

If
n(A) = 9, n(A ∪ B) = 12, and n(B) = 5,
then what is
n(A ∩ B)?

Answer 2

\[n \left( A \cup B \right)=n(A)+n(B)-n(A intersection B)\]
substitute the values and get the solution.