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
```

- Divide both sides by the coefficient 70

```
70x/70 = 50000/70
x = 714
```

How would I write this out as a JavaScript algorithm?

·

Juan Pablo Isaza

You can easily achieve the result as

```
const startWidth = 500;
const percentageWidth = 70;
const result = Math.round((startWidth * 100) / percentageWidth);
console.log(result);
```

·
Juan Pablo Isaza
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