Sub formula()
Dim formulaString As String
Dim I As Integer
Cells(1, "B").Value = Cells(1, "A").Value
For I = 2 To 10
formulaString = "=A" & Trim(str(I)) & "+B" & Trim(str(I - 1))
Cells(I, "B").formula = formulaString
Next I
End Sub