Final answer:
The default number of worksheets in a new Microsoft Excel workbook is 3. This setting is customizable, but the initial configuration provides three worksheets.
Step-by-step explanation:
The default number of worksheet in Microsoft Excel is 3 worksheets when you open a new workbook. This default setting can be customized according to user preferences. For example, in Microsoft Excel 2016 and newer versions, you can set the default number of sheets by going to File > Options > General, and then changing the number under 'Include this many sheets'. However, when you initially install and run Excel without making any changes to the settings, it will open with three worksheets.