n = 20, the number of questions
p = 1/5 = 0.2, the probability of making a correct guess
q = 1 - p = 0.8, the probability of making an incorrect guess.
Expected success = 60% or 6 of 10.
From the binomial distribution,
P(6 of 10) = ₁₀C₆ p⁶q⁴
= 210*0.2⁶*0.8⁴ = 0.0055
Answer: 0.0055
