As a child of the 80's, it was a big deal when my school was one of the few in my area that had a complete computer lab in the library with an Apple II for each student in the class. The catch? All the "games" available all had to do with math or typing. Spielhaus's MindRacer Duel [App Store] provides quite a bit of personal nostalgia, as you're forced to solve math problems on one of three difficulty settings to make your car travel down the race track.
Playing on Easy is, as you would expect- quite easy. Expert mode provides math problems filled with parenthesis and negative numbers, which require a little more brain power to quickly figure out on the fly. MindRacer Duel can be played both single player and two player, and at the current price of free, there's not much reason to not pick this one up if you're looking to brush up your math skills, or have kids that need to learn their multiplication tables.
App Store Link: MindRacer Duel, Free