You are trying to run this game on a device which has insufficient resolution to display the game properly. Just so you know ...
Train arithmetic operations: addition, substraction, multiplication and division. It is not only math; you can practice English at the same time. Instead of numbers, you can play this game with words. For that check 'Convert numbers to text' - you can use it on operation or on result or both. If you decide to use words instead of numbers, make sure your spelling is correct (like seventeen, forty-two, sixty-seven, ... mind those dashes!).
Should the range up to 99 scare you, try up to 20 first.