Flying Saucer Invasion app for iPhone and iPad

"Flying Saucer Invasion" is a game that tests users arithmetic ability and reaction ability.
In the game, there will be a continuous stream of flying saucers flying to the earth. You need to calculate the mathematical formula on the flying saucers before the flying saucers successfully reach the earth.Then select the shell and click the "SHOT" button to launch the shell and destroy the flying saucer.If the flying saucer successfully reaches Earth, the game will fail.Accumulate points to unlock more flying saucers.