Can any one help me on part(b) of the following question. I did part(a)
Q1) In the multiple-choice examination, candidate John picks his answer to each question at random from the list of 3 answers provided, of which only one is correct. A candidate answering 18 or more questions correctly passes the examination.
(a)For a paper containing 45 questions, use a normal approximation to find, to 3 decimal places, the probability that Johns passes.
(b)It is required that the probability that Johns passes should be less than 0.005. Use a normal approximation to show that the paper should contain at most 31 questions.