technically, they are five eighths elf, two eighths human and one eighth maia.
I knew that was wrong, so...
I got sucked into the math, (math is not my strongest suit) and I don't come out with those figures.
Here's my math - am I missing info somewhere? Is Maia blood stronger?
Thingol (elven) + Melian (maia)
Luthien (1/2 elven 1/2 maia) + Beren (human)
Dior (1/2 human 1/4 elven 1/4 maia) + Nimloth (elven)
Elwing (10/16 elven 2/16 maia 1/4 human) + Earendil (1/2 elven 1/2 human)
Elrond (9/16 elven 6/16 human 1/16 maia) + Celebrian (elven)
Elrohir, Elladan, Arwen: ( 25/32 elven 6/32 human 1/32 maia)