If $A = \{x \mid x \text{ is a prime number, } 0 \leq x \leq 9\}$,then the number of elements of the power set of $A$ is

The number of non-empty subsets of the set $\{1, 2, 3, 4\}$ is

In each of the following,determine whether the statement is true or false. If it is true,prove it. If it is false,give a counterexample.
If $x \in A$ and $A \not\subset B$,then $x \in B$

Let $S = \{1, 2, 3, \ldots, n\}$ and $A = \{(a, b) \mid 1 \leq a, b \leq n\} = S \times S$. $A$ subset $B$ of $A$ is said to be a good subset if $(x, x) \in B$ for every $x \in S$. Then,the number of good subsets of $A$ is

Find the union of each of the following pairs of sets:
$A = \{ x : x \text{ is a natural number and a multiple of } 3 \}$
$B = \{ x : x \text{ is a natural number less than } 6 \}$

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