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Fuzzy set theory is circumscribed to the need to broaden the scope of classical mathematics meaning potentiation possibilities of mathematical modeling of real world systems. One can appreciate that the nature of reality and our way of thinking and the symbolism of interpersonal communication languages are also sources of uncertainty, imprecision, vagueness, ambiguity. The imperative of handling properties not necessarily "perfect determinable", namely "vaguely defined" (but with a measurable degree of uncertainty) has led to the imposition of fuzzy sets theory, which proved to be the systematic frame suitable to management of ambiguity and imprecision. Using fuzzy numbers involves some difficulties (related for example to the relaxation of equalities relative to invertible elements) that could be surpassed by using fuzzy numbers characterizing through families of "confidence intervals".