I keep getting a crash where it seems to be hitting continuously. My multiplier is up over 6000 now and the score keeps rolling from positive to negative as the float overflows.
I agree the elemental correspondences seem a little counterintuitive. Since addition and subtraction are inverses, it might make sense their elements are in oppostion (fire/water for example). Similar for multiplication/division. You'd still need to answer the question correctly, but at least it would decrease the twitch-factor of "which one fights void again?"
Once you get an upgrade buggy it gets a LOT easier. The AI seems to not try to run other computer players off the road, but loves to run you off the road.