StarCraft II: Wings of Liberty sold more than a million copies in 24 hours and 1.5 million copies over the first 48 hours of availability, announces Blizzard. They say this makes the real-time strategy sequel the biggest PC game launch of the year, and that this sets a record "for fastest-selling strategy game of all time."
1 mil the first day, 0.5 mil the second day? Uh oh, by the simple law of geometric series, the total number of SC2 sold over its lifetime will be 1/(1-0.5) = 2 million