首先你这个比较多，我这边提供一个方法，算是一个简易版的，希望能举一反三
计算前：
计算后：
前端代码：










计算


后台代码：
using System.Collections.ObjectModel;
using System.Windows;

namespace WpfApplication1
{
///
/// MainWindow.xaml 的交互逻辑
///
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
getdata();
data_datagrid.ItemsSource = daitemsource;

    }
    public class data
    {
        public double fistNumber { get; set; }
        public double secondNumber { get; set; }
        public double thirdNumber { get; set; }
        public double averageNumber { get; set; }
    }
    ObservableCollection<data> daitemsource;
    private void getdata()//在你那应该是读取数据之后赋值给data类各成员，这里是直接赋值了
    {
        daitemsource = new ObservableCollection<data>();
        daitemsource.Add(new data { fistNumber = 5, secondNumber = 60, thirdNumber = 10 });
        daitemsource.Add(new data { fistNumber = 15, secondNumber = 36, thirdNumber = 160 });
        daitemsource.Add(new data { fistNumber = 25, secondNumber = 56, thirdNumber = 710 });
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        foreach (var item in daitemsource)
        {
            item.averageNumber = item.fistNumber + item.secondNumber + item.thirdNumber;
        }
        data_datagrid.Items.Refresh();
    }
}

}

前端代码老发不上去，这边补上