src/Number.php
public function add(Number $addend)
    {
        $resultDecimalValue = $this->decimalValue() + $addend->decimalValue();

        $result = new Number($resultDecimalValue);

        return $result->convert($this->getNumberSystem());
    }
public function add(Number $addend)
    {
        $resultDecimalValue = $this->decimalValue() + $addend->decimalValue();

        $result = new Number($resultDecimalValue);

        return $result->convert($this->getNumberSystem());
    }
Add two number together.
The number-system of the result will be the one of the number
who's was the called object.

@param Number|Number $addend

@return Number