» Calculating a Building's Occupancy Rate at Specified Times

Problem:

Columns B & C show the times that each of a building's tenants left and returned on a particular day.
We want to calculate the building's occupancy rate at each of the times listed in column E.

Solution:

Use the COUNTIF and COUNT functions as shown in the following formula:
=(COUNTIF($C$2:$C$6,">="&E2)-COUNTIF($B$2:$B$6,">"&E2))/
COUNT($A$2:$A$6)