If $A, B$ and $C$ are three sets such that $A \cap B = A \cap C$ and $A \cup B = A \cup C$ then
Show that if $A \subset B,$ then $(C-B) \subset( C-A)$
If $A \cap B = B$, then
Consider the sets $X$ and $Y$ of $X = \{ $ Ram , Geeta, Akbar $\} $ and $Y = \{ $ Geeta, David, Ashok $\} $ Find $X \cap Y$
Let $A =\{1,2,3,4,5,6,7\}$ and $B =\{3,6,7,9\}$. Then the number of elements in the set $\{ C \subseteq A : C \cap B \neq \phi\}$ is