Two sets $A$ and $B$ are disjoint if and only if

If $A = \{1, 2, 3, \ldots, 10\}$,then the number of non-empty subsets of $A$ containing only odd numbers is

If $A \cap B = B$,then

Which of the following is a set? Justify your answer.
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The solution set of the congruence $x \equiv 3 \pmod{7}$ is given by:

Decide,among the following sets,which sets are subsets of one another:
$A = \{ x: x \in \mathbb{R} \text{ and } x \text{ satisfies } x^2 - 8x + 12 = 0 \},$
$B = \{2, 4, 6\}, C = \{2, 4, 6, 8, \dots\}, D = \{6\}$