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It is easier to understand how to calculate that if we do it with simple numbers first.
The 1st step is to calculate the size, for Sector we have 2,3,4 means 3 numbers which can be calculated by
B5: =B3-B2+1
Same for Area
The fraction of Sector / Area is
C6: =B5/C5
All you have to do to answer your question is to write the dates into the cells.
Andreas.