1. Page 1-9 (1digit/page
x 9page) = 9 digits = 9 page
2. Page 10-99 (2digits/page x 90page)= 180 digits = 90 page
3. Page 100-999 (3digits/page x 900page)= 2700 digits = 900
page
2,929 total digits – (9 digits + 180 digits + 2700 digits)= 40
digits
Since there are only 4 digits after page 999 we divide 40/4
= 10, thus there are 10 more pages after 999
So the book has 1009 pages.
Hope
this answer will be a good help for you.
