Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Range("A3")) Is Nothing Then
Application.ScreenUpdating = False
Rows.Hidden = False
Select Case Target.Value
Case 1
Range("10:30").EntireRow.Hidden = True
Case 2
Range("20:30").EntireRow.Hidden = True
End Select
Application.ScreenUpdating = True
End If
End Sub