How do I accomplish this percentage issue

Question

I'm working in JavaScript. I have a graphic done and it is somewhat like this.

100 [=======||=======] 200

So basically this is a kind of mathematical problem. On the left and right side are two numbers, as a range. The 3rd number, in between this range will be defined and the || mark is moved according to this 3rd number.

So in this example the 3rd number is 150, which makes the || divider in the exact middle. What I want is a way to calculate a percentage value from these 3 given numbers to align the || divider through a css left: xx% property. How might I do this?

EDIT: I'm adding the fiddle as told by the users. http://jsfiddle.net/e2dLv/1/

any suggestions/critics about the code are welcome.

It is solved now as answered by Zeta. It may help someone.

Answer 1

This is basically linear scaling with an initial offset:

p = 100 * (value - min) / (max - min)

Note that this assumes that value is in the interval [min, max] and max != min. This gives you the percentage as a number between 0 and 100.