Having trouble adding rows to DataGrid in WPF

I have create a DataGrid in WPF in XAML and now I want to add some rows.   Here is the XAML Code segement

        <DataGrid x:Name="DataGridResults" HorizontalAlignment="Left" Height="171" Margin="68,151,0,0" VerticalAlignment="Top" Width="715" Initialized="DataGridResults_Initialized" SelectionChanged="DataGridResults_SelectionChanged">
            <DataGrid.Columns>
                <DataGridTextColumn x:Name="ColumnMode" Header="Mode"/>
                <DataGridTextColumn x:Name="ColumnCyan" Header="Cyan"/>
                <DataGridTextColumn x:Name="ColumnMagenta" Header="Magenta"/>
                <DataGridTextColumn x:Name="ColumnYellow" Header="Yellow"/>
                <DataGridTextColumn x:Name="ColumnBlack" Header="Black"/>
                <DataGridTextColumn x:Name="ColumnTotal" Header="Total" FontWeight="Bold"/>
                <DataGridTextColumn/>
            </DataGrid.Columns>
        </DataGrid>

It has 6 columns.
I created a Class as

    public class Cost
    {
        public string Mode { set; get; }
        public Single Cyan { set; get; }
        public Single Magenta { set; get; }
        public Single Yellow { set; get; }
        public Single Black { set; get; }
        public Single Total { set; get; }
 
    }

so, to add a row to the grid, i should just do
            DataGridResults.Items.Add(new Cost() { Mode = "Test", Cyan = 0.025f, Magenta = .026f, Yellow = .027f, Black = .028f, Total = .198f });
DataGridsResult is my DataGrid....

I end up with a blank row.  It adds the row, but not populated.  
What am I missing?

thanks!