I'm wondering the origin of deciding a slave was 60% of a person. What was the rationale? I would get 1/2; it makes sense. Was the South 20% better at negotiating than the North? It's a somewhat odd fraction so I'm thinking there'll be an interesting story behind it.
Take a look at this great answer by /u/AnAmenableAnemone. Basically it was a realpolitik move by the Constitutional Convention (specifically, the Committee of Detail) to use a number that had been mostly agreed to during the Articles of Confederation.