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I have two values

startWidth = 500px
percentageWidth = 70%

I'd like to calculate the value of startWidth at when percentageWidth changes, for example if I wanted maxWidth, I'd be working with:

startWidth = ???px
percentageWidth = 100%

To calculate this mathematically is easy, I would just do:

Create an equation that shows the fractional relationship between the percentage and its value. Use the variable x to represent the unknown total.

70/100 = 500/x

Cross-multiply the equation to bring the variable to one side of the equation as a whole number. Multiply values diagonal from each other in the equation, i.e.

70x = 50000

70x/70 = 50000/70
x = 714

How would I write this out as a JavaScript algorithm?

about 4 years ago · Juan Pablo Isaza

Answer question

Accepted Answer · 2022-07-11T06:37:49.086Z

You can easily achieve the result as

const startWidth = 500;
const percentageWidth = 70;

const result = Math.round((startWidth * 100) / percentageWidth);
console.log(result);