'ungetestet !!!!
 
  Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button2.Click
 
        Dim a, b, c As Integer
        static n as integer
        a = Zufallszahl()
 
        TextBox1.Text = a
        n+=1
        if n = 5 then  
 
            stoppuhr.Stop()
 
            dauer = stoppuhr.Elapsed.Seconds
            stoppuhr.Reset()
            TextBox7.Text = dauer
            Button1.Enabled = True
            n = 0
       end if
 
    End Sub