.xls for versions up to Excel 2003 and .xlsx from Excel 2007 onwards.
For workbooks in Excel 2003, the extension .xls is used.
Excel 2007 does use the .xlsx extension for its workbooks.
xlsx is the main extension used for Excel 2007.
.XLS files are standard Microsoft Excel spreadsheet files. .XLT extension is used for the Excel template files. - Neeraj Sharma
XLS is the main extension name used in Excel.
.doc
Microsoft Excel can be used for accounting. Any thing that has maths could be used in Microsoft Excel.
Microsoft Excel.
Microsoft Excel allows you to be pretty<3
Excel 2013 uses a .xlsx extension.
Microsoft Word is used for writing papers, and Microsoft Excel is for spreadsheets.
nobady