protected function generateEquation()
    {
        $ops = [' + ', ' - ', ' * ', ' / '];
        $equation = null;
        $rand1 = rand(1, 10);
        $rand2 = rand(1, 10);
        $op    = $ops[rand(0, 3)];
        // If the operator is division, keep the equation very simple, with no remainder
        if ($op == ' / ') {
            $mod = ($rand2 > $rand1) ? $rand2 % $rand1 : $rand1 % $rand2;
            while ($mod != 0) {
                $rand1 = rand(1, 10);
                $rand2 = rand(1, 10);
                $mod   = ($rand2 > $rand1) ? $rand2 % $rand1 : $rand1 % $rand2;
            }
        }
        $equation = ($rand2 > $rand1) ? $rand2 . $op . $rand1 : $rand1 . $op . $rand2;
        return $equation;
    }