Exclude random cells from SUM

The answer is here: https://support.microsoft.com/en-us/kb/192891

Copying just in case the link goes dead:

The following procedure adds an apostrophe in front of text, values, or formulas in the current selection:

'Appends hidden apostrophe as first character.
'Works on cells with formulas, text, or values.
'Excellent for displaying formulas when printing.

Sub ApostroPut()
    For Each currentcell In Selection
        'Prevents inserting apostrophes in blank cells.
        If currentcell.Formula <> "" Then
            currentcell.Formula = "'" & currentcell.Formula
        End If
    Next
End Sub
				
The following procedure removes the apostrophe in front of text, values, or formulas in the current selection:

'Removes hidden apostrophes that are first characters.
'Works on cells with formulas, text, or values.

Sub ApostroRemove()
    For Each currentcell In Selection
        If currentcell.HasFormula = False Then
            'Verifies that procedure does not change the
            'cell with the active formula so that it contains
            'only the value.
            currentcell.Formula = currentcell.Value
        End If
    Next
End Sub
				
NOTE: You can restore a value that you changed to text by copying the number 1, selecting the cells that contain the text you want to restore, and using the Paste Special command on the Edit menu with the multiplication operation.