var scoreStr = "小明:87;小花:81;小红:97;小天:76;小张:74;小小:94;小西:90;小伍:76;小迪:64;小曼:76";

  var myarr=scoreStr.split(";");

  var myarr1=new Array();

  var sum=0;

  for(var i=0;i<myarr.length;i++)

  {

      sum +=parseInt(myarr[i].substr(myarr[i].indexOf(":")+1));

  }

  document.write("班级总分:"+sum+"<br>")

  document.write("平均分:"+Math.round(sum/myarr.length))