1. **State the problem:** Find the sum of all whole numbers from 1 to 20. 2. **Formula used:** The sum of the first $n$ whole numbers is given by the arithmetic series formula: $$S_n = \frac{n}{2}(t_1 + t_n)$$ where $S_n$ is the sum of $n$ terms, $t_1$ is the first term, and $t_n$ is the $n^{th}$ term. 3. **Apply the formula:** Here, $t_1 = 1$, $t_n = 20$, and $n = 20$. 4. **Calculate the sum:** $$S_{20} = \frac{20}{2}(1 + 20)$$ 5. **Simplify:** $$S_{20} = 10 \times 21$$ 6. **Final answer:** $$S_{20} = 210$$ This means the sum of all whole numbers from 1 to 20 is 210.