|For me, it really depends on the plot and how exciting it is. I can't tell on how fast do I read but I know If based "in one day" depending on the pages and the scenario... lets say...
If the manga is boring... around 2-3 chapter (like if its on 50+pages) 5 chapters (25less pages)
If the manga is exciting... around 6-8 chapter (like if its on 50+pages) 12 chapters (25less pages)
imo, i'm in the average (>_<)> idk if its odd that i posted it like this or not (・_・; ) teehee...
Spoiler (mouse over to view)
If you like you can do the MATH (；一_一) ... i think maybe in a week is around 30 or 85 chapters xD