It is sometimes said that learning probability at an introductory level is not difficult since many probability questions are just questions about proportion. However, students often perform badly on probability questions and one reason for this might be an inadequate familiarity with proportions. In order to investigate this we developed a self-completion test instrument of 10 questions needing an understanding of proportion. Our students took about 25 minutes to complete this test. The questions were arranged with the simpler questions at the start, and the harder questions towards the end. The most difficult question, included partly as a way of finding out which students really did understand probability, asked students to find the chance that a pile of four bricks would reach five high before a pile of three bricks if new bricks were added at random to the two piles, shown as an outline diagram. This question, a version of one discussed by Monks (1985) is best tackled with a tree diagram. All questions, except one, were open-ended.
The CAUSE Research Group is supported in part by a member initiative grant from the American Statistical Association’s Section on Statistics and Data Science Education