If you want to mentally calculate three additions, you need to memorize the result of the addition and then add again. If you don't memorize it well, you will make a mistake.
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[Game overview]
30 questions will be asked.
After answering 30 questions, the number of correct answers will be displayed.
If you answer all 30 questions correctly, the difficulty will increase from the next study. Difficulty is displayed numerically, starting at 1 and increasing up to 22.

[End of game]
After answering 30 questions, you will be finished.
You can end the game at any time by pressing the end button even in the middle of the game.

[About the record]
Difficulty and score are recorded each time. Press and hold the reset button to clear the record and return the difficulty to the initial state.