Acalculus student takes a 20-question, multiple choice test with 5 answer choices for each question. find the mean and standard deviation of the number of questions that he/she gets correct

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

μ=4 ; σ=1.8