To find the unit rate of push-ups per day, you divide the total number of push-ups by the total number of days.
Here’s the calculation:
\[ \text{Push-ups per day} = \frac{40 \text{ push-ups}}{8 \text{ days}} = 5 \text{ push-ups per day} \]
So, the unit rate is 5 push-ups per day.