src/number/Percentage.php
public function of($number)
    {
        $value = clone $this;
        $value->bcmul($number)->bcdiv(100);
        if ($number instanceof Number) {
            $class = get_class($number);
            $value = new $class($value);
        } else {
            if (is_numeric($number)) {
                $value = new Number($value);
            } else {
                throw new \InvalidArgumentException();
            }
        }
        return $value;
    }
public function of($number)
    {
        $value = clone $this;
        $value->bcmul($number)->bcdiv(100);
        if ($number instanceof Number) {
            $class = get_class($number);
            $value = new $class($value);
        } else {
            if (is_numeric($number)) {
                $value = new Number($value);
            } else {
                throw new \InvalidArgumentException();
            }
        }
        return $value;
    }
Percentage OF $number is how much Number?

@param Number|String $number
@return Number
Depending on the input, but always an object extended of Number

@throws \InvalidArgumentException