Counting combinations: The number of ways to choose k items without replacement from a total of n is given by (n choose k) :
Binomial distribution: The probability of obtaining k successes out of n trials given a probability p of success for any one trial is given by:
Hypergeometric distribution: When choosing a random subset of size r from n items of which m belong
in a particular category, the probability that k of the selected items belong to that category is given by:
Standard normal distribution (or Gaussian distribution): The sum of a large number of independent variables follows a normal distribution of density function:
Computing z-scores: Any probability p can be represented as the standard deviations away from the mean of a standard normal distribution corresponding to tail area p.
