A book has 400 pages. How many numbers do you need to number these pages? How many numbers does the number 3 appear in these pages?

Analysis: 1 ~ 9 page number is one digit, ***9 pages, * * * requires digits.

1× 9 = 9 (pieces);

10 ~ 99 pages have two digits, * * * 99-9 = 90 pages, and * * * requires digits.

2× 90 = 180 (piece);

The page number of 100 ~ 400 pages is three digits, * * * 400-99 = 30 1 page, and * * * requires digits.

(400-100+1) × 3 = 301× 3 = 903 (pieces).

In a word, this book needs to be digitized.

9+ 180+903 = 1092 (pieces).

The number of times that Math 3 appears in the page number can be considered in three situations:

When the unit mathematics is 3, there are 0 ~ 9, 10 digits in decimal places, and 0 ~ 3, 4 digits in hundredth digits, so * * *

4× 10 = 40 (times);

When the decimal mathematics is 3, there are 0 ~ 9, 10 digits to fill the unit, and 0 ~ 3, 4 digits to fill the hundred digits, so * * *

4× 10 = 40 (times);

When the numerator is 3, there are 0 ~ 9, 10 species to fill in decimal places, and 0 ~ 9, 10 species to fill in single digits, so * * *

10× 10 = 100 (times).

Therefore, the number of times that Math 3 appears in the page number is:

40+40+ 100 = 180 times.