Chapter 7 - Section 7.1 - Sample Spaces and Events - Exercises - Page 458: 58

$V′∩I$ 25

The set of stocks that did not increased is $V′$ and the set of Internet stocks is called $I$ Therefore the set of Internet stocks that did not increased can be written in a form $V′∩I$ $n(V'\cap I)=n(I)-n(V\cap I)=40-15=25$