I want to quote something from Jacob Milgrom's The JPS Torah Commentary: Numbers (New York: Jewish Publication Society, 1990). This may come in handy when I write my (tentative) paper on the Temple Scroll's interpretation of Numbers 31:25ff.
"Divine decree ordains the division of the persons and animals taken as spoil. The soldiers and civilians each get one-half, from which a levy is exacted for the clergy, the soldiers paying one-tenth as much as the civilians. Specifically, one-five-hundredth of the army's share goes to Eleazar (i.e., the sanctuary) and one-fiftieth of the civilians' share goes to the Levites. The older tradition in the Bible and the ancient Near East is that the temple (and its personnel) receives a tithe (see Gen. 14:20; 28:22). The Koran prescribes that 'to God belongs a fifth' of the spoil (8:42). Here the clergy receives a much smaller proportion, but, considering the huge quantities involved, the amount is substantial.
"David also decrees that the battlefront and home front should divide the spoil equally, and since the text records that 'from that day on it was made a fixed rule for Israel, continuing to the present day' (I Sam. 30:25), it has been suggested that David's rule was retrojected into this account of the war against the Midianites in the wilderness. Yet the Mosaic ruling does not divide the spoils equitably since the clergy receives unequal shares (the Levites ten times as much as the priests). The mathematics is as follows:
"SOLDIERS
(X/2)-(1/500)(X/2)=(499X/1000)
"CIVILIANS
(X/2)-(1/50)(X/2)=(490X/1000)
"Thus for every thousand persons or animals taken captive the soldiers receive nine more than the civilians. The difference, though paltry, is enough for the Temple Scroll of the Dead Sea sectaries to ordain that the clergy should receive its share first, that is, one-thousandth for the sanctuary and one-hundredth for the Levite to be taken from the total spoil; the remainder is then to be divided equally between the soliders and the civilians. In that way, the prescriptions of Moses and David harmonize perfectly" (262).
Milgrom's argument assumes that the Temple Scroll treats Numbers 31 and I Samuel 30 as authoritative traditums (or traditi) that should be harmonized.