<script>

        var btn = document.getElementById('btn');

        var result = document.getElementById('result');

        btn.onclick = function () {

            var num1 = Number(document.getElementById('num1').value);

            var num2 = Number(document.getElementById('num2').value);

            var operate = document.getElementById('operate').value;

            if (operate == '+') {

                result.value = num1 + num2;

            } else if (operate == '-') {

                result.value = num1 - num2;

            } else if (operate == '*') {

                result.value = num1 * num2;

            } else if (operate == '/') {

                result.value = num1 / num2;

            } else {

                result.value = num1 % num2;

            }

        }

    </script>
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