se ho capito bene quello che vorresti fare
codice:
Dim v(10), i, somma, n As Integer
        Dim sommas As String = ""
        Label1.Text = ""
        Label2.Text = ""
        Randomize()
        n = CInt(TextBox1.Text)
For i = 1 To 10
            v(i) = 1 + Int(Rnd() * 3)
            Label1.Text = Label1.Text & v(i) & "-"
            somma = somma + v(i)
            If i Mod n = 0 Then
                sommas = sommas + somma.ToString + "-"
                somma = 0
            End If
        Next
        Label2.Text = sommas
        Label1.Text = Label1.Text.Substring(0, Len(Label1.Text) - 1)
        Label2.Text = Label2.Text.Substring(0, Len(Label2.Text) - 1)