12. To number the pages of an encyclopedia, 6869 digits were required. How many pages are there in it?
12.Note that there are 9 single-digit numbers, 99-9=90 two-digit numbers, digits - 90 × 2=180; 999-99=900 three-digit numbers; digits - 900 × 3=2700. Let's calculate the number of four-digit numbers in the page numbering of the book: 6869-2700-180-9=3980, 3980: 4=995. Adding up the obtained results, we get: 9+90+900+995=1094 pages in the encyclopedia.