nova: 13/13 - but really it is a pretty easy test, the most interesting part was looking at the breakdown of the sample American test takers. I was quite gobsmacked by how few people knew the breakdown of gases in the atmosphere.
If you want something harder (for us kiwis), then do the news iq test:
http://www.pewresearch.org/quiz/the-news-iq-quiz/
I only got 8/13.
Ouch.
The 5 questions I got wrong were all photos of random American politicians (ok well perhaps one of them wasn't quite so random, and I really should have got it right, but I'd be quite impressed if someone here got full marks on that test, without cheating or guessing)
10/13 on the news quiz, most of randoms were guesses