Sounds messy. From what I'm seeing - you'd have to do a running total (running from highest to lowest.) which you divide by the grand total to come up with a "running percentage". And then - make some kind of business rule as to what belongs in which tier.
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Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?