"Mental Math" is a simple and clean Android app for mental arithmetic training. You can practice on your own or challenge friends to compete and improve your skills. The app is open source and respects your privacy. Customizable Training Select which arithmetic operations to include (+, −, ×, ÷). For each operation, choose from nine difficulty levels to customize your training precisely to your skill level. Two Game Modes • Practice Mode lets you complete a fixed number of problems (10, 20, 30, 40, or 50). • Timed Mode challenges you to solve as many problems as possible within a time limit (1, 2, 3, 4, or 5 minutes). Challenge your Friends You can share a game link to: 1. Replay a completed game with the exact same problems to compare scores with friends. 2. Start a new game with preset settings for a fair and fresh challenge for everyone. Difficulty Calculation Problem difficulty is determined using algorithms based on column addition, column subtraction, long multiplication, and long division, creating realistic and well-balanced exercises. Detailed Results After each game, view a detailed summary that includes your selected settings, your performance (accuracy, speed, and score), and a complete list of all your problems and answers for review. Personal Leaderboard Your top 10 results are displayed separately for each combination of settings, allowing you to easily track your progress. You can also review detailed summaries of your top games at any time. Game History Explore the complete history of all your scored games. You can sort the list by time or numerically to find specific games. Anytime, you can revisit any match to view a detailed summary of its results. Practice Reminders Set up periodic reminders to support regular mental math practice. Notifications are sent in the evening (around 6 p.m.) and can be scheduled daily, every three days, or weekly. Clean Design A simple and minimalist app design with no unnecessary elements or distractions, des