You can see the number of opportunities if you mouse-over the stat.
In the Hud you also have the option to enable the Times/Opportunities property in the Hud Editor which will display it as "50% (25/50)".
If you would still like to see the number of opportunities as a separate stat that is certainly possible with a custom stat. Take a look at the Custom Stats Guide
for an overview of how custom stats work. The Tutorial: Custom Reports and Statistics
goes into much more detail (this was written for PT3, but the same principals apply).