average calculation question
 

I am making a sheet to figure the average number of Yes's in column L. Column
L will have either "Yes", "No", Or "DK" (Don't Know) entered into it. Column
C has a persons name in it. Right now I have it set up so that the names and
value from L start on row 6. Rows 1 - 5 are locked in place and used as a
small reports section. In that section I have 3 cells set up to count the
number of Yes, no, and DK's using a simple =COUNTIF(L:L,"Yes") formula. Then
a total field that adds the number of Yes, No, and DK. I then have a field
formatted for % that has "=B1/(B4-B3)" (B1 = # of Yes, B4 = Total, and B3 = #
of DK's) so that it takes the number of Yes and divides that by the total
minus the number of Dk's since I do not want them figured into my %. In Row
5 I also have an auto filter set up so that I can hit the drop down and pick
a specific name from the list so I will only see the rows that pertain to
them.

What I would like to do it make a cell that will calculate a % (kind of like
the "=B1/(B4-B3)" one from above) based off of only the name that I have
picked from my list. So that it will be blank (or show the over all %) when
I do not have a name picked. When I pick "Person 1" from my list then it
will show a % of yes (minus DK) for only that person.

I hope that is enough detail. Let me know if it is not and thank you all
for looking.