Paris is a city of books and bookstores. In the 1970s, 80 percent of French-language publishing houses were found in Paris, almost all on the Left Bank in the 5th, 6th and 7th arrondissements. Since that time, because of high prices, some publishers have moved out to the less expensive areas. It is also a city of small bookstores; There are about 150 bookstores in the 5th arrondissement alone, plus another 250 book stalls along the Seine. Small Paris bookstores are protected against competition from discount booksellers by French law; books, even e-books, cannot be discounted more than five percent below their publisher's cover price.

What percentage of french publishing houses were in Paris in the 1970s?