A textbook has \(1000\) pages. How many of the pages have page numbers whose digits add up to exactly \(4\)?

Guest Feb 14, 2023

#1**0 **

If the textbook has 1000 pages, then the page numbers range from 1 to 1000. To find the number of pages with page numbers whose digits add up to exactly 4, we can use the following formula:

Number of pages = $\sum_{i=1}^{9}$(Number of pages with i as the last digit)

For example, the number of pages with 0 as the last digit is the same as the number of pages with 4 as the last digit, as both digits add up to 4. Similarly, the number of pages with 1 as the last digit is the same as the number of pages with 3 as the last digit, as both digits add up to 4.

Using this formula, we can calculate that the number of pages with page numbers whose digits add up to exactly 4 is 12.

Guest Feb 14, 2023