Strangely, every brand of sandpaper is different. I was sanding a classic Mustang, getting it ready for paint, and for some reason I used the paper that came with a Makita hand sander, it was incredibly robust. The common 3M paper I had on hand was nowhere near as good.
If I were to guess, I'd say 10 discs would do it. But that depends on how much work that paper has to do. Are you just removing the high spots, or are you removing mountains of material and is the floor covered in white colored water?