The number of pages in the book is 203.
Numbers 1 to 9 have 1 digit. This means that 9 pages in the book would have 1 digit. Numbers 10 to 99 have 9 digits. This means that 90 pages in the book would have 18 (9o x 2) digits. Numbers 100 to 199 have 300 (100 x 3) digits. This means that 100 pages in the book would have 3 digits.
Total digits left = 501 - (180 + 9 + 300)
= 501 - 489
= 12
Number of pages left = 12 / 3 = 4
Total number of pages in the book = 9 + 90 + 100 + 4 = 203 pages
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