1. **State the problem:** We are given a six-sided number cube rolled 18 times, and the number two appears 4 times. We want to find the experimental probability of rolling a two. 2. **Formula for experimental probability:** $$\text{Experimental Probability} = \frac{\text{Number of favorable outcomes}}{\text{Total number of trials}}$$ 3. **Apply the formula:** Number of favorable outcomes (rolling a two) = 4 Total number of trials = 18 So, $$\text{Experimental Probability} = \frac{4}{18}$$ 4. **Simplify the fraction:** $$\frac{4}{18} = \frac{\cancel{2} \times 2}{\cancel{2} \times 9} = \frac{2}{9}$$ 5. **Interpretation:** The experimental probability of rolling a two based on the 18 rolls is $\frac{2}{9}$. 6. **Compare with given probabilities:** The given fractions are $\frac{1}{9}$, $\frac{2}{9}$, $\frac{1}{3}$, and $\frac{4}{9}$. Our calculated experimental probability matches $\frac{2}{9}$. **Final answer:** The experimental probability of rolling a two is $\frac{2}{9}$.