Today, Google has made it transparent about what percentage of share is being paid to the Publishers (through Adsense) from what the Advertiser pays Google (through Adwords).
who is a Publisher?
Adsense for Content
If Google takes $100 from an advertiser, for the Ads displayed in Publisher’s websites, $68 is paid to the Publishers and the remaining $32 is for Google’s costs for their continued investment in Adsense.
Read more from Adsense Blog post