TOEIC conversion /20

Hello all,
Beautiful site you have yourselves here.
I'm in the process of marking 250 mock TOEIC papers, and need the grades for Monday. I have my conversion chart of how many correct answers equal what points, but then I have to get that overall score (generally between 600 and 990) into a grade out of 20, as this is in France, and all grades need to be out of 20!
Does anyone know how to convert this? Anyone else in France? Time is running out, quite seriously.....
We used to have something downloaded from the net, but we've moved offices and it's been lost... now I can't find it online - I've tried all sorts of search requests in both English and French, I'm getting desperate!

Thanks a huge bunch in advance.

Simon

AS a rough possibility, divide the score by 990 (the maximum), which will give a number 0.something. Forget the 0. and you've got a percentage (near enough)- divide by 5 and you've got a mark out of twenty.




If you try it with 600 (about 60%):

600/990 = 0.606060606061

0.606060606061/5 = 0.121212121212. Grab the first two digits- 12/20
(Use the next digit or two for half marks, etc.)

(12/20 = 60%.)

I don't know if there are better ways, but this one seems to do the job.