Explanation:

- The mean of the first 5 books is 430, so the total pages in these books is \( 5 \times 430 = 2150 \) pages.

- The mean of the last 5 books is 380, so the total pages in these books is \( 5 \times 380 = 1900 \) pages.

- The mean of all 9 books is 400, so the total pages for all books is \( 9 \times 400 = 3600 \) pages.

- To find the fifth book's pages, add the pages of the first and last 5 books then subtract the total pages:

$$

\text{Total pages for first 5 books} + \text{last 5 books} - \text{all 9 books}

= 2150 + 1900 - 3600 = 450

$$

- Therefore, the number of pages in the fifth book is 450.