[ExGeeEye]

Like most compromises involving numbers, it probably started with a high number on one side (the south giving in on 10/10 and demanding 9/10, and the north giving in on nada and offering 1/10), it gets all the way to 7/10 on the southron side and 1/2 on the northern, and then split the difference.

I don't know, of course, but that makes sense to me.

[Billthedrill]

I don't normally weigh in on these threads because there really isn't much point, but I can speak to the 3/5 Compromise. It was a legacy from, of all things, a tax proposal that was to amend the Articles of Confederation, and it was the idea of James Madison, who was rather bitter about it being turned around to be applied to political representation during the Constitutional Convention some four years later. (See Federalist #54). It was never in effect during the Confederation government because it failed to obtain the unanimous approval that such amendments required under the Articles.

The ironic thing is that had the slaves been granted 5/5 representation, the extra representatives accorded the slave-holding states would have been highly unlikely to vote their interests. And had they been granted 0/5 representation, they'd have been only property. Ethically the thing was a lot more complicated than it looks.