Geometric mean

The average that fits ratios and compounding — ⁿ√(x₁·x₂·…·xₙ).

The geometric mean is the right average for ratios, growth rates and compounding.

Try this

b (with a = 4)

geometric mean = √(4·b) = 6

Formula

GM =^{n} x_{1} \cdot x_{2} \cdot \dots \cdot x_{n}

Try it

GM of 4 and 9

√(4·9) = √36 = 6.