JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div id='example' ng-app=''>
  <input ng-model='number1' type='number'>
  <select ng-model='operation' ng-options="op for op in ['+', '-', '/', '*']"></select>
  <input ng-model='number2' type='number'>
  <div ng-if="operation == '+'"><div id='output' ng-bind="number1 + number2"></div></div>
  <div ng-if="operation == '-'"><div id='output' ng-bind="number1 - number2"></div></div>
  <div ng-if="operation == '/'"><div id='output' ng-bind="number1 / number2"></div></div>
  <div ng-if="operation == '*'"><div id='output' ng-bind="number1 * number2"></div></div>
</div>