excel - adding XX% to a range of cells
 

Alright, I'm trying to make custom price lists, I have everything in a few different spreadsheets (about 15000 different product sku's, that my company sales). I know that I would have to do this to each spreadsheet but...


I know how to put a button an excel spreadsheet, I want to enter a percentage into lets say cell A1 and then click a button to ADD the additional percentage to the cost in all of the cells in a range say from cell b2 through b5000

is there a way to do this, I really dont want to have to start all of these spread sheets all over!

is anyone as confused as I just made myself :) ?? :)