A multiple choice test with 4 independent questions was given to a student who attended the class by a complete mistake, thus knowing nothing about the subject. Each question had 5 possible answers, and the student needed to answer at least 4 questions correctly to pass the test. (i) Find the mean number of correctly guessed problems.
(ii) Find the standard deviation of this probability distribution.
(iii) What is the maximum non-significant number of guessing correctly?