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.
Alternatively, use the formula:
P(x) = C(n,x)*px*(1-p)n-x
Where C(n,x) represents the number of combinations of taking n things, x at a time.