DC,
You can sort the serial numbers in ascending order. This
will ensure that duplicates appear in consecutive rows.
Then go to the first empty column to the right of your
data and type in a conditional statement that identifies
the duplicates - Example: If(a1 = b1,1,0). Copy this
formula down to the end of your data. Now you have a "1"
next to each record that contains a duplicate serial
number.
Convert this new column to values (select the entire
column, then Copy / Paste Special / Values over to the
next column. Now you can sort the records by the new
column you created (descending order), and all the
duplicates are at the top of your sheet.
If you delete all the duplicates (the rows with a "1" in
the new column), you will be left with only one of each of
those serial numbers in your spreadsheet.
b.