var tech=[
    {name:"android", rate:0,bar:10},
    {name:"angular", rate:0,bar:10},
    {name:"node", rate:0,bar:10},
    {name:"maven", rate:0,bar:10},
    {name:"log", rate:0,bar:10},
    {name:"vs2019", rate:0,bar:10}
  ];
  $scope.tech=tech;
  $scope.incrementRate= function(t,r)
  {
     t.rate=r;
     t.bar=parseInt(t.bar)+Number(r); //giving NaN
     alert(t.bar); //giving undefined
  };

<table>
<tr>
         <td>Select course:</td>
         <td><select class="form-control contact-text" name="course" ng-model="tech.name">
           <option ng-repeat="t in tech"
        ng-value="t.name">{{t.name}}</option>
         </select> <br> </td>

       </tr>
       <tr>
         <td>Rate:</td>
         <td><input type="radio" class="ml-3" name="rate" value="1" checked ng-model="tech.rate"> 1
             <input type="radio" class="ml-3" name="rate" value="2" ng-model="tech.rate"> 2
            <input type="radio" class="ml-3" name="rate" value="3" ng-model="tech.rate"> 3
            <input type="radio" class="ml-3" name="rate" value="4" ng-model="tech.rate"> 4
            <input type="radio" class="ml-3" name="rate" value="5" ng-model="tech.rate"> 5
            </td>
       </tr>
       <tr>
         <td colspan="2" style="text-align:center"><br> <br>
           <button type="submit" name="rate" class="btn btn-primary"
           ng-click="incrementRate(tech,tech.rate)">Rate</button></td>

       </tr>
     </table>
<!-- for eg, -->
Android:
    <div class="wrapper">
      <div class="android skills" ng-style="{'width':tech[0].bar+'%'}">
  {{tech[0].bar+'%'}}
      </div>
      </div>