A helpful customer has reported a problem in version 2.2 of CardDroid Math. If you go to the “Built-in Problem Sets” screen of the “Recent Problem Sets” screen and tap the system back button (hardware button or bottom edge of the screen), CardDroid Math will unceremoniously crash. The workaround is to tap the big blue “Back” button toward the top of the screen. Version 2.3 is now available and looking rock solid!
Sorry for any inconvenience,
Steve @ WhitneyApps