Water Triangle
Benjamin Dickman, https://twitter.com/benjamindickman/status/1305023104033468416?s=20, wrote an article in which this device was used in a lesson for proportional reasoning. https://www.researchgate.net/publication/321683932_Creativity_in_Question_and_Answer_Digital_Spaces_for_Mathematics_Education_A_Case_Study_of_the_Water_Triangle_for_Proportional_Reasoning/link/5b96d1b492851c78c4126534/download
I had to make one.
What question would you pose to learners playing with it?
