Maths Amarda by Dick Smith Electronics is an educational game for learning simple math.
You are the cannon at the bottom of the screen. And you have to destroy 20 ships that will start from the right side of the screen and swim over to the left side. If any ship reaches the left side, you have been invaded and lost the game.
Each ship has 2 numbers on its sail. One over the other. The numbers will contain from 1 to 5 digits. Each ship will fly a flag with x , + , - or / in it. This is the type of sum you should be doing with numbers.
As you type, your answer will appear in the lower right corner of the screen. After you have entered your answer, you fire the key from the cannon. You move the cannon left or right with the < less than > and < more > keys. If you collide with a ship and you get the correct answer, it will be sunk.