The benefit/cost (B/C) ratio method is utilized in many government and public work projects to determine if the expected benefits provide an acceptable return on the estimated investment and costs. Many authors have studied probabilis- tic cash flows in recent years. They introduced some analytical methods which determine the probability distribution function of the net present value and in- ternal rate of return of a series of random discrete cash flows. They considered serially correlated cash flows and the uncertainty of future capital investment and reinvestment rates and they presented some formulae for the B/C ratio for probabilistic cash flows. In the paper, the expected value and the variance of a probabilistic cash flow are obtained by means of moments. Then a probabilistic B/C ratio is given. Fuzzy set theory has the capability of representing vague knowledge and allows mathematical operators and programming to be applied to the fuzzy domain. The theory is primarily concerned with quantifying the vagueness in human thoughts and perceptions. The fuzzy B/C ratios are devel- oped for a single investment project and for multiple projects having equal or different lives.
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The main area which Formal Safety Assessment (FSA) methodology was created for is maritime safety. Its model presents quantitative risk estimation and takes detailed information about accident characteristics into account. Nowadays, it is broadly used in shipping navigation around the world. It has already been shown that FSA can be widely used for the assessment of pilotage safety. On the basis of analysis and conclusion on the FSA approach, this paper attempts to show that the adaptation of this method to another area-risk evaluating in operating conditions of buildings-is possible and effective. It aims at building a mathematical model based on fuzzy logic risk assessment with different habitat factors included. The adopted approach lets us describe various situations and conditions that occur in creating and exploiting of buildings, allowing for automatic control of the risk connected to them.
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