John needs to take an examination, which is organized as follows: To each question 5 answers are given. But John knows the correct answer only with probability 0.6 . Thus, with probability 0.4 he has to guess the right answer. In this case, John guesses the correct answer with probability \(1 / 5\) (that means, he chooses an answer by chance). What is the probability that John knew the answer to a question given that he did answer the question correctly?