does abacadaba or dial down the middle work on multiple choice exams?

Answer 1

If the answers are truly random, picking one letter for all the answers should get you 25% correct if the choices are A through D.

However, on most exams the answers are not random. Maybe a SAT or GRE exam is randomized but the 20 question quiz your teacher creates has whatever biases s/he has in selecting the answers. As an example, I had a professor who gave us a 20 question quiz. Every answer was A - until question #20 which was some other answer. My professor wanted to know if people would pick A for #20. As it turned out, many students suspected A was the wrong answer for #20 but since the answer for the previous 19 questions was A, they went against their better judgment and chose A. That was an interesting experiment in human nature.

Answer 2

when in doubt, mark C. it's the most often used letter.