OK a geometric mean is the nth root of the product of the numbers.
SO there are 2 number so you will take the square root of (1/3)*(27)
the calculator do the math part.
$${\sqrt{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right){\mathtt{\,\times\,}}\left({\mathtt{27}}\right)}} = {\mathtt{3}}$$
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