# Can't figure out the exact function requirement

I need a function which is roughly (but not exactly) equivalent to $$f(x)=\frac{1}{x}$$ As $x$ varies from $0$ to $100$, $f(x)$ should vary from $20$ to $0$. Rough indications for values are as follows, to give an idea and know if I know things right:

\begin{array}{c|*5c} x& 4& 11& 20& 50& 80\\ \hline f(x) &18 & 15 & 12 & 5 & 2 \end{array} I am completely out of touch of maths. Please if someone can at least guide me in the right direction. I have filled several pages of notebook and now I'm getting confused.

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$f(x) = \frac{(x-100)^2}{500}$ works pretty well. It's a parabola with its vertex at $(100,0)$ such that $f(0) = 20$.