How are these numbers calculated?

Big Games

How we did last week and who we should root for this week.   Explain

Week of 4/20100.0*Chance in playoffs100.0*Average seed
Gloucester 28 Saracens 23 -2.3
Worcester 26 Harlequins 42 In
+0.1
Northampton 47 Sale Sharks 7 -0.0
Week of 5/4100.0*Chance in playoffs100.0*Average seed
Harlequins 22 Northampton 19 +0.3
Leicester 32 London Irish 20 -0.1
Games Above .500
Chance Will Make Playoffs