Examine whether the following statement is true or false:
${1, 2, 3} \subset {1, 3, 5}$

In the following,state whether $A = B$ or not:
$A = \{ x: x \text{ is a multiple of } 10 \}$
$B = \{ 10, 15, 20, 25, 30, \ldots \}$

State whether the following set is finite or infinite:
The set of letters in the English alphabet.

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

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 $A \not\subset B$ and $B \not\subset C$,then $A \not\subset C$.

Consider the sets $\phi, A = \{1, 3\}, B = \{1, 5, 9\}, C = \{1, 3, 5, 7, 9\}$. Insert the symbol $\subset$ or $\not\subset$ between the pair of sets: $B \dots C$.