If $A$ and $B$ are disjoint,then $n(A \cup B)$ is equal to

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

If $A = \{x : f(x) = 0\}$ and $B = \{x : g(x) = 0\}$,then $A \cap B$ is

Which Venn diagram represents the truth of the statement "All students are hard working."
Where $U$ = Universal set of human beings,$S$ = Set of all students,$H$ = Set of all hard workers.

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

Two dice are thrown. The events $A, B$ and $C$ are as follows:
$A:$ getting an even number on the first die.
$B:$ getting an odd number on the first die.
$C:$ getting the sum of the numbers on the dice $\leq 5$.
Describe the event $A \cap B^{\prime} \cap C^{\prime}$.