Express the inverse proportionality with the formula, knowing that its graph passes through a point: P (0,1; 200).

The function that expresses inverse proportionality is y = k / x. It is only necessary to find the value of the constant k. According to the condition of the problem, the graph of the function passes through a point with coordinates (0.1; 200), that is, at x = 0.1 y takes the value 200. Substituting these values into the formula, we get:

200 = k / 0.1; k = 200 * 0.1; k = 20.

Therefore, our answer is: y = 20 / x.