Thanks for your help. You have the correct understanding, however I was looking for a way to avoid a 40 level Case formula. A Case formula solution does not allow for any changes that only affect future records without adjusting previously created records.
I am also not understanding how a summary field in the parent records helps me if I am going to use a Case formula. Why not just put the Case formula in the child record based upon the total for each child record? I am looking for this markup % to end up on each child record to arrive at a sale price for each child. The total cost and total sale will summarize on the parent record.
I was thinking I would need a separate Markup table related to the parent but then I don't know how to select the correct record in this Markup table based upon a calculated number.