Calculator.php

<?php

class Calculator
{    

    /**
     * Add multiple argument
     *
     * @return int
     */
    public function add()
    {
        $numbers = func_get_args();

        $numbers = array_filter($numbers, function ($num) {
            return is_numeric($num);
        });

        return array_sum($numbers);
    }

    /**
     * Multiply between 2 arg
     *
     * @return int
     */
    public function multiply()
    {
        $args = $this->validateParam(func_get_args());
        list($num1, $num2) = $args;
        
        return $num1 * $num2;
    }

    /**
     * Substract between 2 arg
     *
     * @return int
     */
    public function substract()
    {
        $args = $this->validateParam(func_get_args());
        list($num1, $num2) = $args;
        
        return $num1 - $num2;

    }

    /**
     * Div between 2 arg
     *
     * @return int
     */
    public function division()
    {
        $args = $this->validateParam(func_get_args());
        list($num1, $num2) = $args;

        return $num1 / $num2;
    }   

    /**
     * Validate method params
     *
     * @return array
     */
    protected function validateParam()
    {
        $args = func_get_args();
        $args = $args[0];
        
        if(count($args) > 2) {
            throw new Exception("Just 2 number");
        }

        return $args;
    }
}

// Usage

/*
$cal = new Calculator;

echo 'Add 20 + 30 + 1 = ' . $cal->add(20, 30, 1) . "<br>";
echo 'Multiply 12 * 3 = ' . $cal->multiply(12, 2) . "<br>";
echo 'Substract 12 - 3 = ' . $cal->substract(5, 3) . "<br>";
echo 'Div 100 : 2 = ' . $cal->division(100, 2) . "<br>";

*/