1. **Problem statement:** A man buys an article for 10% less than its value and sells it for 10% more than its value. We need to find his gain or loss percentage. 2. **Let the value of the article be** $V$. 3. **Buying price (B.P.)** is 10% less than $V$, so: $$ B.P. = V - 0.10V = 0.90V $$ 4. **Selling price (S.P.)** is 10% more than $V$, so: $$ S.P. = V + 0.10V = 1.10V $$ 5. **Gain or loss** is calculated as: $$ \text{Gain or Loss} = S.P. - B.P. = 1.10V - 0.90V = 0.20V $$ 6. Since $S.P. > B.P.$, the man makes a gain. 7. **Gain percent** is: $$ \text{Gain \%} = \frac{\text{Gain}}{\text{B.P.}} \times 100 = \frac{0.20V}{0.90V} \times 100 = \frac{0.20}{0.90} \times 100 = 22.22\% $$ **Final answer:** The man gains approximately 22.22%.