Abstract
In IT project management, reserve is the important element for risk resolution. However, we hardly see quantitative method about how to decide the amount of reserve. Three-point estimate method is useful one to estimate risk, but it is insufficient for decision of reserve only to calculate expectation by formula E=(o+4m+p)/6. The expectation formula means that probability distribution of estimated value follows beta distribution, so we have calculated a concrete probability distribution. It describes that relation between reserve and success probability, and it provides quantitative information to decide the amount of reserve, for example, 'is the amount of reserve sufficient?' or 'how much is valid reserve?'.
