Customizing low stock alert for different situations

Instead of displaying the actual # of units that are available for the low stock alert, I would like to create custom item #'s. Here is the logic:

IF: actual inventory = less than 10, display actual inventory

IF: greater than 9, less than 20, display (.75)actual inventory

IF: greater than 19, less than 30, display (.40)actual inventory

IF: greater than 29, less than 40, display (.30)actual inventory

IF: greater than 39, don't display.