This is a very simple experiment I designed to demonstrate the diminishing marginal returns problem for my students. I welcome any feedback.
https://www.economicsnetwork.ac.uk/iree/v7n1/vazquez-cognet.pdf
Vazquez-Cognet, Jose (2008) The Production of Mathematical Problems: A Diminishing Marginal Returns Experiment International Review of Economics Education 12/2008; 7(1):103-116.