What a delight to train in mental calculus with this app ! I bought the full version with pleasure, even if the drawings of the girls are not that much pretty. My level after one week ? 70 000 th out of 1 100 000 players. One week later, I am "Queen of Maths" (highest level), 26 000 th out of 1 100 000 players. Now, it becomes more difficult. To go over 6 million points and come closer to 10 million points, you have to score on each chapter of each book, a better mark than last time. Very very challenging... A pure addictive delight for the brain. Yummy !