Suppose the student guesses the answers, we shall consider this a binomial probability problem of success. This implies that getting a question right is p=1/5.
The number of questions is n=20 questions.
The mean of binomial distribution is
mean=n*p= 20*1/5=4
b] The standard deviation of a binomial distribution is given by:
σ=√(n*p*(1-p))
=√(20*0.2*0.8)
=1.79~1.8
Answer:
μ=4 ; σ=1.8