Backwards preload

I have a preloader that works. Its going 0 to 100%…

I want my preloader bar alpha to get to 0 as it progresses

For example, its preloaded 25% so the preloader alpha is 75%…its preloaded 50%, the preloader alpha is 50%…its preloaded 75%, the alpha is 25% etc…how can I do that?