1. **Problem:** Identify the relationships among the number systems: natural numbers ($\mathbb{N}$), whole numbers ($\mathbb{W}$), integers ($\mathbb{Z}$), and rational numbers ($\mathbb{Q}$).\n\n2. **Explanation:** Natural numbers are the counting numbers starting from 1, whole numbers include all natural numbers plus zero, integers include whole numbers and their negatives, and rational numbers are numbers that can be expressed as a fraction $\frac{a}{b}$ where $a,b \in \mathbb{Z}$ and $b \neq 0$.\n\n3. **Example:** $5 \in \mathbb{N} \subset \mathbb{W} \subset \mathbb{Z} \subset \mathbb{Q}$.\n\n4. **Real-life application:** Counting apples (natural numbers), including zero apples (whole numbers), debts and credits (integers), and sharing pizza slices (rational numbers).