In the previous papers, a strict method of calculating electric resistance of a binary particles system was described. In that method, the total electric resistance was calculated by applying Kirchhoff's law.
In the present paper, in order to simplify the calculation of total electric resistance (R) of a binary system, an approximation (series and parallel) method was proposed whereby R could be calculated rapidly without any trouble of overloading a computer system. The symbol R (total electric resistance) presented in the previous papers was now rewritten as R_K in order to draw a distinction from the value of approximation (R_S). This approximation method is considered particularly applicable to a binary particles system containing a large number of particles. Furthermore, its application is effective when the difference in electric resistance between two groups of particles is not so much. In such a case, R_S can be calculated rapidly even by a computer which has not so large capacity.