turn values around

Hello!

Probably a simple yet tricky questions here:
(this mathematical solution goes beyond my understanding)

I have a Spotlight and want to control the value of its spotAngle.
And here it comes:

Example:

When my range is 30 (for instance) my spotAngle needs to be 1.
But otherwise when my range is 1, my spotAngle needs to be 30.
When * range* is 15, spotAngle needs to be 2.
When * spotAngle* is 15, * range* needs to be 2 etc.

This is to keep the same spotAngle size on an object that will vary in range.

Here’s a piece of my script (a_distance comes from a raycast somewhere else):

public void AddLength(float a_distance)
	{
		spotlight.range = a_distance;
		spotlight.spotAngle = ?????? ; 
	}

Wouldn´t that be something like:

spotlight.spotAngle= 30 / spotlight.range;

Or did I get your question wrong?