Understanding "decimam decimae"

Question

I'm struggling to see the logic behind the expression "decimam decimae". In the Vulgata, we read (Numbers 29: 11-13):

In calendis autem offeretis holocaustum Domino, vitulos de armento duos, arietem unum, agnos anniculos septem immaculatos, et tres decimas similae oleo conspersae in sacrificio per singulos vitulos: et duas decimas similae oleo conspersae per singulos arietes: et decimam decimae similae ex oleo in sacrificio per agnos singulos: holocaustum suavissimi odoris atque incensi est Domino.

I get the tres decimas and duas decimas, which are pretty much identical to Spanish. However, the expression decimam decimae is meant to mean one tenth. So, my questions:

1. Is decimam decimae an expression or it is literally to mean one tenth? Wouldn't it mean a tenth of a tenth, which is 1/100 (in that (1/10)*(1/10)=1/100), instead of 1/10?

2. Would using una decima be a valid, and perhaps more natural expression?

Answer 1

It's hard to disagree with fdb's response that decimam decimae should mean "a tenth of a tenth", but that doesn't apparently reflect the meaning of the passage. I think the problem arises with misunderstanding the Hebrew, which is:

עִשָּׂרוֹן עִשָּׂרוֹן לַכֶּבֶשׂ הָאֶחָד לְשִׁעַת הַכְּבָשִּׂים

This get translated in the LXX quite literally as:

δέκατον δέκατον τῷ ἀμνῷ τῷ ἑνὶ εἰς τοὺς ἑπτὰ ἀμνούς

This doesn't seem to make much sense in Greek, but reflects the Hebrew quite literally.

It looks to me like Jerome tried to improve the sense by representing עִשָּׂרוֹן עִשָּׂרוֹן ("tenth tenth") as decimam decimae, rather than follow the LXX δέκατον δέκατον.

FWIW, the Jerusalem Bible translates this as "one-tenth for each of the seven lambs". (My own command of Hebrew is insufficient to comment on the original construction.)

Answer 2

decimus is "tenth" (ordinal number)

decima (pars) is "one tenth" (fraction)

decima decimae is "a tenth of a tenth".