StarSum app for iPhone and iPad

StarSum is a game to practice addition and subtraction of 2 digits. It contains 4 expressions. Each expression has 3 operands and 2 operators.

There are 4 circles along the right side. These circles show the results of these 4 expressions.
1. The top 2 circles show the results for the top pair of 2 expressions.
2. The bottom 2 circles show the results for the bottom pair of 2 expressions.
3. The goal of this game is to swap the operands to make the top 2 expressions have the same results and the bottom 2 expressions have the same results.

4. The player could choose to practice plus only or the combination of plus and minus.
5. It supports 5 levels.
Level 1: the player needs to swap 4 operands.
Level 2: the player needs to swap 5 operands.
Level 3: the player needs to swap 6 operands.
Level 4: the player needs to swap 7 operands.
Level 5: the player needs to swap 8 operands.