# Problem 7.3 (7 points)

A piece has fallen out of a dictionary, the first page of which is numbered 213, and the number of the last page is written with the same digits in some other order. How many pages are in the missing piece?
# Solution:

The number of the last page is 312 (it must be even). Then the number of pages is 312 - 212 = 100.

| Criteria | Points |
| :--- | :---: |
| Correct solution | 7 |
| Calculated 312 - 213 + 1 = 100, without explaining why 1 is added | 6 |
| Obtained the answer 99 | 4 |
| Noted the different parity of the first and last pages, without further progress | 2 |
| Incorrectly determined the number of the last page | 0 |

Answer: 100 pages (50 sheets)