Harmonic mean is expressed as the reciprocal of the arithmetic mean of the reciprocals of the given set of observations.
Example: Harmonic Mean of numbers 1, 5, 9 is given by:
= 3 / 1.31
The generic formula for Harmonic mean of positive real numbers is give by:
Harmonic mean of two numbers X and Y is given by:
H = 2XY / (X + Y)