@Gummo, Okay, but a negative denominator like 5/-3 should be fine the way it is. And obviously 5/-1 won't return -5 in this app since the answer spot is a fraction so it's not gonna spit out a whole number. But the Fraction class itself simplifies it to -5 if you use the simplify and getString methods.
I agree, it is hard to see the high score. Cool game, though and well coded. I think you should make it gradually faster to make it more challenging however. Great job though!
So if you do like, [3] [OVER] [5] [-] [1] [OVER] [4] [=], it returns 7/20.
I'm not gonna post the code here though, I hope to eventually get in the iPhone Developer Program so I can sell some apps.