Comment by robochat

Actually, I can't seem to get the maths to work. Isn't it just the Binomial distribution? Each question has 5 options so the probability of 'success' is 1/5 and so to get 19 questions 'specifically wrong' out of the 45 planted questions by chance is just (1/5)*19 * (1-1/5)*26 * 45!/(19!26!) = 1 in 2588 but in the article it is 1:100. What am I doing wrong ?