First you have to define perimeters of Binomial distribution.
n - how many trials/questions do you have
p - probability guessing right answer to each question
x - how many successes do you expect.
Assuming the 6 questions are independent,
n=6 (questions)
p=probability of guessing the right answer (1/5)
x=exactly the number of successes over the 6 questions (2).
Look up the appendix table, or the Excel function to calculate the probability.
