Because the pages of this book are equal, we can know that 35+40+(45+50+...)+35 = (45+50+...)+40 From the equation, we can see that there are more brackets after the equal sign than before it. On page 35+40+35-40=70, both brackets start from 45, and the latter is 70 more than the former, that is to say, the former bracket is finally added to 65, and the latter bracket is finally ... 65+70, so the latter bracket is 70 more than the former one. Because there are two kinds, it is reasonable to go back to the question. Methods Both 35 and 40 read on the last day are less than 70. We can know that the brackets in front are added after 65, and then 70 is brought in casually. We can conclude that the page number of this book is 35+40+45+50+55+60+65+35=385.