<div id="vuetest">
 <table>
 <tr>
 <td>数学</td>
 <td><input type="text" v-model.number="math"></td>
 </tr>
 <tr>
 <td>物理</td>
 <td><input type="text" v-model.number="physics"></td>
 </tr>
 <tr>
 <td>英语</td>
 <td><input type="text" v-model.number="english"></td>
 <tr>
 <td>总分</td>
 <td>{{sum}}</td>
 </tr>
 <tr>
 <td>平均分</td>
 <td>{{average}}</td>
 </tr>
 </tr>
 </table>
 </div>

var vuetest = new Vue({
 el:'#vuetest',
 data:{
 math:'',
 physics:'',
 english:'',
 },
 computed :{
 sum:function () {
 return parseFloat(this.math)+this.physics+this.english; 
  },
 average :function(){
 return Math.round(this.sum/3);
  } 
 }
 });