Through a probability problem, a connection is showed between binomial distribution and negative binomial distribution and therefore a composed formula is set up, which is proved by way of probability and algebra.

• 摘要通过一个概率问题，给出二项分布与负二项分布的一种联系，从而建立一个组合公式，并由概率思维方式与代数方式给出证明。