Identify Top/Bottom 10% using an equation

Hi,

I need to be able to use an equation to identify the top/bottom 10% by month and year. I need an equation that looks at raw data and goes ok here are all the pieces for Feb FY18 of these 100 cells here are the 80 that you should count.

Every month will have a different top/bottom 10%.

For example, in April FY18, there are 37 lines. Rounding up i need to identify the top/bottom 4 lines.
My goal is to be able to do a month over month pivot, averaging category 1, and filtering out the top/bottom 10%

Thanks!

The top/bottom 10% of the total number of lines for the month/year.
For example in April, there are 37 lines of data. 10% of 37 is 3.7. Sorting Category 1 from smallest to largest. I would then remove the 4 smallest and the 4 largest.

I need to be able to have the equation go in a data set, here are all the items for this month. There are x number in this month. 10% of that number is y. Determine which are the smallest/largest and identify the y of that group

Category 1 FY Month Count
1 FY18 April N
1 FY18 April Y
2 FY18 April Y
2 FY18 April Y
3 FY18 April Y
4 FY18 April Y
10 FY18 April Y
90 FY18 April Y
91 FY18 April Y
100 FY18 April N

10 lines of data x 10% = 1 Remove the smallest/Largest by the qty 1
So the average goes from 30.4 in Category 1 to 25.375

I want to identify the outliers of the average by taking the total number of lines for that month x 10% and not including the smallest/largest numbers by qty monthx10%