Here Binomial distribution to be used because two mutually exclusive outcomes occurrence(here attempting the advanced terrai

Here Binomial distribution to be used because two mutually exclusive outcomes occurrence(here attempting the advanced terrain) and non-occurrence(here not attempting the advanced terrain) are possible for each visitor

Here the formula used is the Probability mass function of binomial distribution

P(X=x) =  where p is the probability of success, q= (1-p) probability of failure, r = 0,1,2,…..,n

Here in all cases n =20