Excellent calculations, RobertR, but what you forgot to factor into the equation were these:
(1)G- (2)B= -30 This approximates the average trip to a record store:
I bought one good (G) CD and the other two sucked - (2)B - equalling two unlistenable albums in your collection and a loss thirty dollars (-30). This negative factor simultaneously also subtracts 4.6 square inches from your living space.
You also forgot this CD collection factor:
+15Y= 0 X (4)BOC This is the outgrowth factor, where after fifteen years (+15Y) , zero is the number of times you will listen to your four (4) Blue Oyster Cult (BOC) albums.
Owning about 600 CDs, and applying these variables, I would say I now have +40 listenable albums in my collection, whereas record companies have used my -8,400($) on home improvements in Malibu.