Q.Write the set $B = \{x : x \in \mathbb{Z},\ -3 \le x < 2\}$ in roster form and state $n(B)$.

A set is a well-defined collection of distinct objects; its members are its elements, with $x \in A$ meaning $x$ belongs to $A$ and $x \notin A$ meaning it does not. Because elements are distinct and unordered, $\{2, 2, 3\}$ is just $\{2, 3\}$ and $\{2, 3\} = \{3, 2\}$. A set can be written in roster form (listing the elements, e.g. $\{1, 3, 5\}$) or set-builder form (stating the common property, e.g. $\{x : x \text{ is odd}, x < 6\}$). Standard number sets have fixed symbols: $\mathbb{N}, \mathbb{W}, \mathbb{Z}, \mathbb{Q}, \mathbb{R}$.