$A$ die is thrown. Describe the event $A$: a number less than $7$. Find $A \cup B$ if $B$ is the event of getting a number $3$.

Let $A = \{a, b, c\}, B = \{b, c, d\}, C = \{a, b, d, e\}$. Then $A \cap (B \cup C)$ is:

If sets $A$ and $B$ are defined as follows:
$A = \{ (x, y) : y = e^x, x \in R \}$
$B = \{ (x, y) : y = x, x \in R \}$
Then:

If $A = \{3, 5, 7, 9, 11\}$,$B = \{7, 9, 11, 13\}$,$C = \{11, 13, 15\}$,and $D = \{15, 17\}$,find $(A \cap B) \cap (B \cup C)$.

In a class of $140$ students numbered $1$ to $140$,all even-numbered students opted for the Mathematics course,those whose number is divisible by $3$ opted for the Physics course,and those whose number is divisible by $5$ opted for the Chemistry course. The number of students who did not opt for any of the three courses is:

If $A$ and $B$ are disjoint sets,then $n(A \cup B) = $