A batch of books were delivered to the bookstore, and 7 / 12 of them were sold on the first day. Another 170 copies were sold on the second day, and 180 copies remained. How many books are there in total?

After 7 / 12 is sold, the remaining 5 / 12 is 170 + 180 = 350, 350 divided by 5 / 12 is 840

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