Today it seems to be about 40.
I'm 51 so I remember when the rock stations played all the songs above.
I set up a Jefferson Starship station on Pandora and thumbed up some of the older Marty Balin hits and all of the sudden, the station started playing all kinds of great 70s hits that I hadn't heard in years. Stuff like this:
At one time they were hits. Now you never hear them. In an endless ocean of Stairway..., Free Bird, and More Than A Feeling, these tunes have fallen from playlists.
I'll start off with this gem. Is it rock? Is it disco? Is it funk? All I know is it has awesome harmony vocals and a great guitar/sax solo.