I guess 42 will be a spike in the results - but it would be interesting to verify ;)
Are you implying than the average HNer or Redditer has a different bias wrt the average girl?
Stipulate that both digits must be distinct and odd, then guess 37.
or distinct and even, then guess 68 (think this was an old david blaine trick if i recally correctly)
Just make her pick a number between 1 and 10, you'll have at least 10 times more success probability.
And it will be 10 times less impressive.
So clearly we should have her pick a number between 1 and 1000!
43 is actually not bad. I would think that most people would pick something somewhere in the middle. A somewhat similar distribution as with the 1-10 results. Odd numbers more often than even numbers. Prime numbers even more often.