You can try something like the following:
Code:
Sub Delete_Rows_LEssThan20()
Dim iRow
Dim iMaxRow
iMaxRow = ActiveSheet.Cells.SpecialCells(xlCellTypeLastCell).Row
For iRow = 1 To iMaxRow
If iRow > iMaxRow Then Exit Sub
If Val(ActiveSheet.Cells(iRow, 3).Value) < 20 Then
Rows(iRow).EntireRow.Delete
iRow = iRow - 1
iMaxRow = iMaxRow - 1
End If
Next iRow
End Sub
Cheers
Shasur