The underground crystal mine is full of resources that you can get by solving math problems – this time you have to face the effects of subtraction. With this application you will be able to practice your subtraction skills on three levels of difficulty, ranging from 10, 20 or 100. The trolley will only fill with crystals if you choose the correct answer by touching it with your hand or foot. As in “Adding”, the number of actions is displayed at the bottom of the screen, while the possible answers are displayed in the center. Can you handle subtraction as well as adding?