1. **Problem:** Simplify the expression $$\frac{a - b}{ab} + \frac{b - c}{bc} + \frac{c - a}{ca}$$ 2. **Formula and rules:** To add fractions, find a common denominator. Here, the denominators are $ab$, $bc$, and $ca$. The least common denominator (LCD) is $abc$. 3. **Rewrite each fraction with denominator $abc$:** $$\frac{a - b}{ab} = \frac{(a - b)c}{abc}$$ $$\frac{b - c}{bc} = \frac{(b - c)a}{abc}$$ $$\frac{c - a}{ca} = \frac{(c - a)b}{abc}$$ 4. **Combine the fractions:** $$\frac{(a - b)c + (b - c)a + (c - a)b}{abc}$$ 5. **Expand the numerator:** $$ac - bc + ab - ac + bc - ab$$ 6. **Simplify the numerator by canceling terms:** $$ac - ac - bc + bc + ab - ab = 0$$ 7. **Final result:** $$\frac{0}{abc} = 0$$ **Answer:** The expression simplifies to 0.