Here binomial distribution to be used because two mutually exclusive

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