To find the experimental probability that the next pizza sold will have pepperoni, we can use the formula for experimental probability:
\[ P(\text{event}) = \frac{\text{Number of successful outcomes}}{\text{Total number of trials}} \]
In this case, the number of successful outcomes (pizzas with pepperoni) is 4, and the total number of trials (total pizzas sold) is 6.
So, the experimental probability \( P(\text{pepperoni}) \) is:
\[ P(\text{pepperoni}) = \frac{4}{6} \]
Now, we can simplify this fraction:
\[ \frac{4}{6} = \frac{2}{3} \]
Thus, the experimental probability that the next pizza sold will have pepperoni is:
\[ P(\text{pepperoni}) = \frac{2}{3} \]