A bookstore owner went to the book wholesale market to buy some books. I bought some books at 1200 for the first time. And sell it for seven dollars at the price in the book. Quick sale

Take the purchase price of the first book as X.

1200/X+ 10 = 1500/X * 1.2

1200 * 1.2/X * 1.2+ 10 = 1500/X * 1.2

1500/ 1.2X- 1440/ 1.2X = 10

12X=60

X=5 yuan

The first time I bought a book, the price was 5 yuan, and I bought 1200/5=240 books.

The total selling price is 240*7= 1680.

Second purchase of 240+ 10 yuan.

When 200 copies were sold for the first time, the total selling price was 200*7= 1400 yuan.

The next 50 books are priced at 40% discount: 50*0.4*7= 140 yuan.

Earned for the first time 1680- 1200=480 yuan.

Earned for the second time1400+140-1500 = 40 yuan.

Earned 480+40 twice = 520 yuan.