Michael,

Adapt the following
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Private Sub Selection_Change()
'selection.value , 'selection = the dropdown boxes name

Select Case Selection.Value

Case 1
Worksheets("Data").Range("a1:c1").EntireColumn.Hid den = True
Worksheets("Data").Range("d1:e1").EntireColumn.Hid den = False

Case 2
Worksheets("Data").Range("a1:c1").EntireColumn.Hid den = False
Worksheets("Data").Range("d1:e1").EntireColumn.Hid den = True

Case 3

End Select
End Sub

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David