Negative Binomial Distribution

The negative binomial distribution counts how many tries it takes to reach a target number of successes, extending the geometric (which stops at the first success) to several.

Write NegBinomial(successes, p), or NegativeBinomial(successes, p), where successes is the whole-number target:

NegBinomial(5, 0.4)

counts the tries needed to reach 5 successes at 40 percent each. Use it for the number of attempts to accumulate a set number of good outcomes.