Best mental arithmetic calculation apps.36+49-26 = ? Can you do the math above in few seconds? By using the abacus mental method, all the people can do it fast and accurately.Abacus Adventure Features: Full tutorial of how to use abacus. Using the abacus method mentally, train up mental calculation in more systematic and faster way. You will be able to handle more complicated calculation in the future. 55 stages in this game, including all the training and tutorials. A normal course of abacus mental cost you $500 or more, you got to save a lot of money and time by using this amazing app. Unlocks the stages, save the princess, collect the coins and more fun!! This app is designed by qualified mental abacus teachers and tested by hundreds of students. Best for children age 5+.