• # question_answer 1) If $\mathbf{n}\left( \mathbf{U} \right)=\mathbf{700},\mathbf{n}\left( \mathbf{A} \right)=\mathbf{200},\mathbf{n}\left( \mathbf{B} \right)=\mathbf{300}$, and $\mathbf{n}\left( \mathbf{A}\cap \mathbf{B} \right)=\mathbf{100}$, then $\mathbf{n}\left( \mathbf{A}'\cap \mathbf{B}' \right)=$ A) 400                              B) 350          C) 300                              D) 600

[c] $\therefore n\left( U \right)=700$ $n\left( A \right)=200$ $n\left( B \right)=300$ $n\left( A\cap B \right)=100$ $\because n\left( A\cup B \right)=n\left( A \right)+n\left( B \right)-n\left( A\cap B \right)$ $=200+300-100=400$ Now, $n\left( A'\cap B' \right)=n\left( A\cup B \right)'$ $=n\left( U \right)-n\left( A\cup B \right)=700-400=300$ Hence, option is correct.