Javascript Function To Calculate How Much To Reduce by Percentage

This functions works perfect if you have want to calculate the reduced percentage of a number.

For example, if you have an image and you want to reduce that image from its original size by 80 perfect. 

If you have an image with the following dimensions: 371x400 we can calculate the image dimensions if we needed to reduce the image to 80%

The JavaScript Code:

function reduceByPercentage(originalSize,Percentage){
   a = originalSize
   a = a / 100;
   b = a * Percentage;
   b = Math.round(b);
   return b;
}

 Usage:

reduceByPercentage(371,80);

Demo:

Image Width Size
Reduce %

Results: