In many practical situations system availability or unavailability is found or given as a polynomial with terms which are mixed products of availabilities and unavailabilities of the components. Starting with such a polynomial, considerable algebraic manipulation has been considered to be necessary before the failure frequency could be determined. Here it is shown that such manipulations are unnecessary. A very easy-to-remember rule immediately produces failure frequency, once system availability or unavailability is given as a polynomial of the type mentioned above.