To find the unit rate of apartments per floor, you would divide the total number of apartments by the number of floors.
So, you can calculate it as follows:
\[ \text{Apartments per floor} = \frac{\text{Total apartments}}{\text{Number of floors}} = \frac{65 \text{ apartments}}{5 \text{ floors}} = 13 \text{ apartments per floor} \]
Therefore, there are 13 apartments per floor.