"Rolling Ball" or "Stones Trap" is an educational game with the arithmetic calculations in the range from 0 to 100. The game is inspired from ancient battle defensive engine. When attacked by the enemies, the highland people often put big rocks on the ridge beside the line of march of the enemies. When the men arrive, they push the stone rolling down to kill the enemy as well to prevent them from passing by.

Based on this idea, the game is designed for players to pull a heavy object (the ball) up high, then drop it rolling down the slope so that it hits the "enemy". The enemy here is the correct answer to math problems. In some cases there may be multiple correct answers, and then just hit on any of them to score. The questions are designed for 4 different content levels from 1 to 4 with the arithmetic problems: counting, addition, subtraction, multiplication, division, comparison numbers from 1 to 100. This games helps learning and practice of basic mathematical thinking become attractive, interesting and challenging!