I think a very important part of learning math is learning that it's not magic or memory, it's just mechanical procedure transforming inputs to outputs (and the

I think a very important part of learning math is learning that it's not magic or memory, it's just mechanical procedure transforming inputs to outputs (and therefore the output must contain the input). I.e., you aren't just teaching the test, you are also improving understanding. Now consider a question like "length of alpha, beta=2, gamma=3, a) sqrt(2^2+3^2) b) sqrt(2+3), c) 2^2+3^2, d) 7". Using your heuristic the student can rule out (d) and has a 33% chance of getting the right answer. The test reveals (averaging this over many questions) that they know a little bit, but nothing close to 100%.