Books are generally regarded as 1 here, because 40% of the books were read on the first day (40% is equal to 2/5), so 3/5 were not read, and because the remaining 5/9 were read the next day, the remaining 3/5 here is the remaining 3/5 on the first day, so they were read the next day.

The second formula is1-2/5-1/3 = 4/15.

Here, I read 2/5 on the first day, 1/3 on the second day, and subtract what I read one or two days ago with the unit 1, that is, I didn't read the rest in the end.

The third formula is 32/4/ 15= 120.

Because as shown in the title, there are 32 unread pages at last, which corresponds to the unread 4/ 15 in the second formula above. If we assume that this book has x pages.

Then it is 32/4/ 15=X/ 1.

X equals 120, which is the total number of pages in this book.