Solution:

Assume that is the number of correctly answered questions out of a total of twenty.

Since the ‘head’ of the coin represents the correct answer and the ‘tail’ represents the incorrect answer. Bernoulli trails are thus formed by repeated tosses or correctly answered questions.

Thus, and

Here, it can be clearly observed that has binomial distribution, where and

Thus, , where

Probability of at least 12 questions answered correctly