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
