It would be best if a sample is attached with say, at least 30 rows of data. My understanding of your problem anyway is on how you will substitute or replace the quantity of the lowest decile with the mean so how about copying the sheet containing the actual data to another sheet then enter a formula in the lowest decile that picks up the mean in the first sheet? If you are making a one time projection of $sales based on the mean, a hard coded formula will do but if you want results where the decile dynamically change with any change in the actual sales, you must provide a data with expected results as I am sure we have several experts here who will happily share their own solutions or point to you the better approach to solving your problem.