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For you are aware that we consume more imported corn than any other nation. Now the corn that comes to our ports from the Black Sea is equal to the whole amount from all other places of export. And this is not surprising; for not only is that district most productive of corn, but also Leucon, who controls the trade, has granted exemption from dues to merchants conveying corn to Athens, and he proclaims that those bound for your port shall have priority of lading. For Leucon, enjoying exemption for himself and his children, has granted exemption to every one of you.
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See what this amounts to. He exacts a toll of one-thirtieth from exporters of corn from his country. Now from the Bosporus there come to Athens about four hundred thousand bushels; the figures can be checked by the books of the grain commissioners. So for each three hundred thousand bushels he makes us a present of ten thousand bushels, and for the remaining hundred thousand a present of roughly three thousand.To help his audience in this piece of mental arithmetic, Demosthenes divides his 400,000 into two parts, of 300,000 (of which the thirtieth is easily calculated) and of 100,000, the thirtieth of which is 3333 1/3 or roughly 3000. It should be remembered that the medimnus is more strictly about a bushel and a half.