math game. Add and subtract to 20. 'Dannyboy' has to complete 5 correct exercises in each world before he gets the key to open the next door. So he can go to the next world. If there is an error, you will hear a different sound and a new exercise will be started. The errors are displayed at the end of the exercise. There are 10 worlds, so he needs 10 keys (50 correct exercises). First touch the question mark with 'Dannyboy'. Fill in results with the small arrows (top is more, bottom is less). Co