Answer: -2 per day.
Explanation:
Given: During a 2-day period, Paul and Alissa's stock price had a change of -4.
Thus, Change in stock = -4
Time period = 2 days
The average change in a subject is given by :-
![\text{Average change}=\frac{\text{total change}}{\text{time period}}](https://img.qammunity.org/2020/formulas/mathematics/high-school/98d456qamtaj0iccnq9ljh8fca4foj4f1o.png)
Therefore,
![\text{Average change}=\frac{-4}{\text{2}}\\\Rightarrow\ \text{Average change}=-2](https://img.qammunity.org/2020/formulas/mathematics/high-school/sevjdnvnghoeynpk7960nf9amaj7mbbcom.png)
Hence, The average change per day = -2 per day.