Calculate the value of $G$ as a combined proportions of $A$, $B$ and $C$

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I have been tasked with an exercise that looks simple but now I have some doubts and I would like to get another opinion.

G is related with A, B and C in the following way.

      _G_
   +/     \-
   /       \
+/  \+   +/  \-
A    B   C    B
  • When $A$ and $B$ increase $G$ increases
  • When $C$ increases and $B$ decreases, $G$ decreases
  • The effect of $B$ on $A$ and $C$ is asymmetric. An increase of $B$ on $A$ makes $G$ increase at a much faster rate. On the other hand, an increase in $C$ would cause $G$ to decrease but at a much lower rate.
  • The value of $A$, $B$ and $C$ go from 0 to 1.

As an example, let's say that $A=0.8$ $B=0.012$ $C=0.9$. How would you calculate $G$? I would be tempted to simply say

$G=\frac{AB}{\sqrt{C}}$

but I think I missing something since it looks like this is a combined proportions problem.