"your mother" was the first answer but I'd rather say that it's about 0.8. Of course, it depends on the type of carpet and the nature of the rubber surface. Is it a shag pile carpet or a tightly...
You need two different materials to determine the coefficient of friction. Without another material you cannot know what the coefficient of friction is.
Check the following webiste and scroll down the large coefficient of friction table.
http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm
The table contains COF valus for rubber on...