If $A=\{1,2,3,4\}, B=\{3,4,5,6\}, C=\{5,6,7,8\}$ and $D=\{7,8,9,10\} ;$ find

$B \cup C$

If $A$ and $B$ are not disjoint sets, then $n(A \cup B)$ is equal to

If $A$ and $B$ are two sets such that $A \subset B$, then what is $A \cup B ?$

Let $A$ and $B$ be sets. If $A \cap X=B \cap X=\phi$ and $A \cup X=B \cup X$ for some set $X ,$ show that $A = B$

( Hints $A = A \cap (A \cup X),B = B \cap (B \cup X)$ and use Distributive law )

If $A, B$ and $C$ are any three sets, then $A – (B \cap C)$ is equal to