One way:

Put this in your worksheet code module:

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
With Range("Off_Num")
If Not Intersect(.Cells, Target) Is Nothing Then
Application.ScreenUpdating = False
Rows("9:28").Hidden = True
If IsNumeric(.Value) Then
Rows("9:9").Resize(CLng(.Value)).Hidden = False
End If
Application.ScreenUpdating = True
End If
End With
End Sub


In article om,
wrote:

I'm designing a form where Cell A5, which is named Off_Num. This cell
has Values (Select One, 1 to 20) in a dropdown, and Rows 9 to 28 are
hidden.

Now if 1 is selected in Off_Num cell then, the code should Unhide Row
9. And if 2 is selected then Row(9:10) should be unhidden so on, till
if 20 is selected the Rows(9:28) should be unhidden. And if Select One
option is selected that Rows(9:28) should get hidden again.

Please help me with this.