SumElemet

string path = Server.MapPath("App_Data/new.xml");
XElement xe = XElement.Load(path);//导入XML文件
//用LINQ查询Person元素
IEnumerable<XElement> element = from ee in xe.Elements("Person")
select ee;
//计算年龄合计
decimal oldSum = element.Sum(itm => Convert.ToDecimal(itm.Element("Old").Value));
//输出查询元素的值
Response.Write("年龄合计:"+oldSum.ToString()+"<br/>");