How to save Excel file in .xls format? (the old version)
While having your Excel file opened, click on the button on the upper left corner of the program, then select Save as -> Excel 97-2003 Workbook.
2007 excel:
2010 and newer excel:
While having your Excel file opened, click on the button on the upper left corner of the program, then select Save as -> Excel 97-2003 Workbook.
2007 excel:
2010 and newer excel: