That "3000 punched cards" statement was what I'd call "advertising language", mixing in a lot of usage assumptions, and effectively comparing apples with pears.
A standard punched card could hold 80 columns of data, with each column typically representing 1 possible character of a text line. Each column consisted of 12 places, so you might call it 12 bits, but the encoding didn't use all possible combinations.
On a floppy disk, with a different encoding, you typically have 1 byte per character, and represent lines by inserting carriage return and/or line feed characters in between the lines, so you typically get the text in a packed form.
Probably they based their calculation on an assumed average text line length around 25 characters plus line separator, giving roughly 80000 bytes.
If you were to squeeze the maximum out of the punched card medium, you`d get a raw 12*80 bits = 120 bytes. But punching too many holes into the card hurts its mechanical stability, so I guess you'd have to limit yourself to 10 bits per column (with a clever encoding avoiding too many holes), resulting in 100 bytes. Based on that calculation, one floppy equals 800 punched cards, but when advertising the shiny new technology called "floppy", 3000 is much more impressive, isn't it?