Flexor the Mighty! said:
Not quite... here's the full nasty family tree...
Elrond married Celebrian, who was the daughter of Galadriel and Celeborn (and thus is a full-blooded elf). Thus, Arwen's mother's heritage is easy... 100% Elven.
Elrond is trickier... Elros and Elrond were brothers. They were called "half-elven" and were the sons of Earendil and Elwing, both of whom are also called half-elves.
Earendil was the son of Tuor, one of the great men in the first age, and Idril, an elf. Thus, Earendil is fully half-elven.
Elwing was the daughter of Dior and Nimloth. Dior, whom you may or may not recognize as the son of Beren and Luthien, was clearly half-elven, as Beren and Luthien were human and elf, respectively. Nimloth was (as far as we can tell) a full-blooded Elf.
That makes Dior half-elven and Nimloth full-elven... so Elwing would be 3/4 elven.
If Elwing is 3/4 elven, and Earendil is 1/2 elven, that makes Elros and Elrond 5/8 elven and 3/8 human.
Elros chose to become human and was the progenitor of the kings of Numenor (if memory serves). This is why the Numenoreans are so long-lived. Elrond, of course, chose to become elvenkind, and was granted immortality.
This makes Arwen 13/16 elf, for those keeping score at home.
This also makes Galadriel Arwen's grandmother. Celebrian was wounded by poison, and had to leave Middle Earth by way of the Gray Havens or die from the poison, which is why she's not around. This also explains Galadriel's keen interest in the Arwen/Aragorn storyline (in FotR:EE and TTT).
Also, if memory serves, there were 37 generations from Elros to Aragorn, making Aragorn and Arwen first cousins 37 times removed.
No, I don't have a life. And I admit, I had to look up Elwing's heritage...
http://www.glyphweb.com/arda/default.htm
Also, look up the Elessar (the gem Arwen gives to Aragorn in the movies) in Lost Tales some time. Neat stuff for PJ to include in the movie... a "throwaway" for those not familiar with ITS story, but a touch that shows how much of Tolkien he kept track of.
--The Sigil