Classic game of 24! In Custom mode, you can set a level to practice in -- from 1 (normal) to 10 (insane), but in Normal mode, the difficulty ramps up. Use all 4 numbers once to build the number 24 with addition, subtraction, multiplication and division. Solving each problem correctly gives you points according to the level you're on; you win by getting 24 points in one game!
Custom settings also has an All Numbers mode, in which you build the random number (from 1 to 100) in the top left corner instead of 24.
Hint: All problems has at least one correct answer!