Question

Se n( A U B) = 14, n(A) = 10 , n(B) = 9, então n( A ∩ B) é igual a:

Answer 1

$\mathtt{n(A\cup\,B)=n(A)+n(B)-n(A\cap\,B)}\\\mathtt{14=10+9-n(A\cap\,B)}\\\mathtt{n(A\cap\,B)=19-14}$

$\huge\boxed{\boxed{\mathtt{n(A\cap\,B)=5}}}$