Private Sub CommandButton2_Click()

Dim a As Long, b As Long

a = IIf(Cbx1_1.Value = "Yes", 1, 0) + IIf(Cbx1_2.Value = "Yes", 1, 0) +_
IIf(Cbx1_3.Value = "Yes", 1, 0) + IIf(Cbx1_4.Value = "Yes", 1, 0)

b = 4 - IIf(Cbx1_1.Value = "N/A", 1, 0) - IIf(Cbx1_2.Value = "N/A", 1, 0)_
- IIf(Cbx1_3.Value = "N/A", 1, 0) - IIf(Cbx1_4.Value = "N/A", 1, 0)
OUTBX1.Text = Format(a / b, "00.00%")
MultiPage1.Value = 1
End Sub

=ERRORIF (b=0) then MultiPage1.Value = 1 else
    OUTBX1.Text = Format(a / b, "00.00%")