Let $A=\{1,2,3,4,5,6\} .$ Insert the appropriate symbol $\in$ or $\notin$ in the blank spaces:
$ 5\, .......\, A$
Which of the following are sets ? Justify your answer.
The collection of all natural numbers less than $100 .$
Let $A$ and $B$ be two non-empty subsets of a set $X$ such that $A$ is not a subset of $B$, then
Which of the following are sets ? Justify your answer.
A collection of most dangerous animals of the world.
In the following state whether $\mathrm{A = B}$ or not :
$A = \{ x:x$ is a multiple of $10\} ;B = \{ 10,15,20,25,30 \ldots \ldots \} $