State whether each of the following set is finite or infinite :

The set of numbers which are multiple of $5$

Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?

$\{ \{ 3,4\} \}  \subset A$

State whether each of the following set is finite or infinite :

The set of lines which are parallel to the $x\,-$ axis

Let $S=\{1,2,3, \ldots, 40)$ and let $A$ be a subset of $S$ such that no two elements in $A$ have their sum divisible by 5 . What is the maximum number of elements possible in $A$ ?

Write the following intervals in set-builder form :

$\left[ { - 23,5} \right)$

Let $A=\{a, e, i, o, u\}$ and $B=\{a, i, u\} .$ Show that $A \cup B=A$