lol holy shit that's bad for Inferno. Also, will this be the worst 1st to 3rd movie drop of all time? Total domestically, Inferno will drop 80% from Da Vinci Code.
No. Studios treat sequels with more respect now (at least from a budget/marketing perspective), but that wasn't always the case. Assuming a $16M opening and $45M finish for Inferno, the drop from the first to third film would be 79.3%
Big Drops that I can think of off the top of my head:
Jaws to Jaws 3D: $260M -> $45.5M
Beverly Hills Cop 1 to 3: $235M -> $43.6M
Exorcist to Exorcist 3: $193M -> $26M
Home Alone to Home Alone 3: $286M -> $30.9M
EDIT: Some others browsing BOM
Look Who's Talking to LWT Now: $140M -> $10M
Blair Witch Project to Blair Witch: $141M -> $20.5M
Porky's to Porky's Revenge - $105M -> $20.5M
EDIT 2: This also ignores films that went on to have a bunch of straight-to-video sequels. For instance, there are 5 Bring it On films.