We observe that the chances of him getting any one question correct is 1/5, or 20% and of course, the chance of him getting it wrong would be 4/5, or 80%. Find the probability that he gets all 6 questions wrong first. By independent, we can simply multiple and get $0.8^6$. So that chance that he gets at least 1 question right is the complement of the previous probability, or $1-0.8^6$.