The harmonic mean H(x_1, ..., x_n) of n numbers x_i (where i = 1, ..., n) is the number H defined by 1/H congruent 1/n sum_(i = 1)^n 1/x_i. The harmonic mean of a list of numbers may be computed in the Wolfram Language using HarmonicMean[list].
HarmonicMean