Xiao Li is reading a math story book. The number of pages she has read is 90 pages less than the total number of pages, and the number of pages she has not read is 200 pages less than the total number of pages. How many pages are there in this book? 90+200=290

The first condition is that 90 pages are missing, and the antonym of "read" is 90 pages that have not been read;

The second condition, 200 pages less, "I haven't read it" means I have read 200 pages;

So, the 90+ 200 that I haven't seen is ***290 pages in total.