No it's not, he says some of the answers were obviously wrong, but he did the binomial analysis on 45 questions. If you plant 45 answers in a 80 answer test and

No it's not, he says some of the answers were obviously wrong, but he did the binomial analysis on 45 questions. If you plant 45 answers in a 80 answer test and they're mostly obviously wrong then the students who cheat are going to fail either way, so it can't really be true that they were wrong. And if the answers were very obviously wrong then the probability of choosing the wrong answer for each would be much higher than assuming a 20% chance of matching the fake answer. So the whole 1in 100 is highly questionable. To put it another way, let's say he planted only wrong answers, and we have an idiot student that always gets the questions wrong. Now the probability of matching the planted answer has clearly jumped, right? On the flip side, if the planted answers are right, and in general you expect your class to pick correct answers (ie, they're going to pass) then the probability they pick the same as the cheat answer could be as high as 90%