Answer
0.5
half of the stocks that decreased were Internet stocks
Work Step by Step
The table shows that $n(D\cap I)=15$
and $n(D)=30$
$\frac{n(D\cap I)}{n(D)}=\frac{15}{30}=\frac{1}{2}=0.5$
It represents that half of the stocks that decreased were Internet stocks.