Scale inverse to slider position

1

I have a var that captures a slider position like this:

var sliderPosition = Math.round((thumb.y-bounds.top)/(bounds.right-bounds.top)*100);

which outputs a number between 0 and 100 starting on 0. I need to scale an mc from 1 at sliderPosition =0 to .42 at sliderPosition = 100.

Is there a math function that will help me do this?

sorry for the vague explanation. help will be appreciated.

Thanks!