Making a math game to move along the number line presents some challenges. The first is how to move your character if they are sitting on the number line. You could have a series of number buttons like “plus one”, “minus one”, “plus two”, “minus two”. This solution has a couple of problems. First it flirts with understanding negative numbers. Secondly the number line is used to model an abstract problem like 9-3, so the purpose of the game is to reinforce this modeling.
So I decided to present the full problem such as 9-3, 9-2 etc. on the multiple choice buttons. In this way the player can look at the number line for the number they are on and where the opening in the rock is and tie that back to an abstract problem like 9-3. If you are on 9 and the opening is on 6 then 9-3 will get you through the opening.
Add in an opposing kayak which slowly gets faster and the race is on!