What is rhythm and blues music? What is hip hop music?

I was always told that rhythm and blues was like a different type of
jazz-influenced music that is supposed to soothe the mind (like the
song "If I ain't got you" by Alicia Keys) I always thought hip hop was
music that was somewhere between pop and rap (you know, like Katy
Perry's "California Gurls" featuring snoopdog) Do I have this right or
am I confused?

But wait, if these types of music are so different, then how come
modern rhythm and blues are sometimes classified with hip hop?