Let $A = \{1, 2, 3, 4, 5, 6\}$. Insert the appropriate symbol $\in$ or $\notin$ in the blank space:
$2 \dots A$

Write the following as intervals: $\{x : x \in \mathbb{R}, 0 \le x < 7\}$

Which of the following is an example of the null set?
$\{ x : x \in \mathbb{N}, x < 5 \text{ and } x > 7 \}$

In a city,no two persons have an identical set of teeth,and there is no person without a tooth. Also,no person has more than $32$ teeth. If we disregard the shape and size of the teeth and consider only the presence or absence of a tooth at each of the $32$ positions,then the maximum population of the city is:

Determine the subset for the set $\{n(n+1)(2n+1) : n \in \mathbb{Z}\}$.

If $A = \{x \in R : x^2 - 5|x| + 6 = 0\}$,then find $n(A)$.