Given:n = 4a = 8, b = 6, c = 12 and d = 4n = number of observationa, b, c, d are observationsFormula:Harmonic mean= \(\frac{n}{\frac{1}{a}+\frac{1}{b}+\dots +\frac{1}{n^{th}\ term}}\)Calculation:Harmonic mean= \(\frac{4}{\frac{1}{8}+\frac{1}{6}+\frac{1}{12}+\frac{1}{4}}\)= \(\frac{4}{\frac{3+4+2+6}{24}}\)= (24 × 4)/15 = 32/5= 6.4? The harmonic mean of these observations is 6.40 The harmonic mean is the reciprocal of arithmetic mean