Deduct Percentage if Value In Between

Hey guys,

I need some help with this query, I'm not quite sure what would be the most efficient / easiest way of doing so.

I have the following query:
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Okay so what I want to be able to do if MINUS a certain percentage from GrossPay if the GrossPay is in between 2 certain values.

For example, if GrossPay were inbetween $400 and $500 (including ($400 and $500) deduct 10% from the GrossPay.
I would like to make a table of values in between and percentages.

Eg values inbetween:
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How could I create another table, so that for example when I wanted to change the deduction rate of $400 to $501 I could do so just by changing a eg a value in a Field in a table, instead of changing all this code in a query IIf statement.

Or will I just have to hard code this as an IIf statement in a query, and whenever I want to change the percentage deduction of a certain value I will just have to edit this code. I am really hoping that I could avoid this, as I prefer the table approach which would allow me to change percentages on the fly.

Thanks