## How many pages does the book have?

Since there are 9 1-digit natural numbers, 90 2-digit numbers and 900 3-digit numbers are required:

9 digits to number the first 9 pages;

90 x 2 = 180 digits to number the following 90 pages;

900 x 3 = 2700 digits to number the following 900 pages.

Like 180 + 9 <852 <2700 then the x number of book pages has 3 digits and satisfies the equation:

3 (x-99) + 189 = 852

The book has 320 pages.

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