James gets bored with his game so decides to play a different one.  That game promises 100 hours of gameplay but 80% of that is boring grinding.  However, the expansion does add another 30 hours of enjoyable gameplay.  How much enjoyable gameplay does James get?
The first game was 100*.8=<<100*.8=80>>80 hours of grinding
So it was 100-80=<<100-80=20>>20 hours of good gameplay
The expansion brought the time of good gameplay to 20+30=<<20+30=50>>50 hours
#### 50