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Dear AnnieMa, Good Afternoon.

Now than I could see your Worksheet, it´s was VERY EASY to solve the question.
I spent just a few seconds to create a new formula.

You have x and y at a different cells.
It´s make all the diference.

The new formula is MORE SIMPLE, QUICKER and MORE EASY to adapt to another cells if necessary.

The new worksheet is he http://www.4shared.com/document/KHmW...r_CONC_CA.html

Please, take a look at it and tell me if it helped you.

Feel free to ask anything about it.

Ps.: I am from Brazil (Country), Minas Gerais (State), Belo Horizonte (City)
Where are you from?