13. Neat Pete numbered all the pages of a notebook from 1 to 192. Vasya tore out 25 sheets from this notebook and added up all 50 numbers written on them. Could he have obtained the number $1998$?
13. Since the first page in the torn block has an odd number and the last page has an even number, the total sum must be odd. Therefore, the number 1998 could not have been obtained.