Let's start by determining the total number of pizza slices consumed by Ethan and his 7 friends. Together, they make 8 people.
If each person had 5 slices of pizza:
\[ \text{Total slices of pizza} = 8 \text{ people} \times 5 \text{ slices/person} = 40 \text{ slices of pizza} \]
Now, we know that the total amount of food (pizzas and mozzarella sticks) is 64 pieces. To find out how many mozzarella sticks there were, we can subtract the number of pizza slices from the total amount of food:
\[ \text{Total mozzarella sticks} = \text{Total food} - \text{Total slices of pizza} \] \[ \text{Total mozzarella sticks} = 64 - 40 = 24 \text{ mozzarella sticks} \]
Now, to find out how many mozzarella sticks each person ate, we divide the total number of mozzarella sticks by the number of people:
\[ \text{Mozzarella sticks per person} = \frac{\text{Total mozzarella sticks}}{\text{Number of people}} = \frac{24}{8} = 3 \]
Thus, each person ate 3 mozzarella sticks.