Would be good to have an activity to introduce the concept of decimal numbers.
Can also cover (with derived activities) addition/subtraction and potentially multiplication/division?

The idea is to split the screen into 2 rectangles, the top rectangle is the drop area where we can drop units in, (representing the answer),
and the bottom rectangle will always contain a 1 unit consists of 10 parts, and an arrow defining how much the user want to drag to the top rectangle.
mock up : https://imgur.com/a/aMgvuCO