There are multiple ways to include slide numbers in PowerPoint. You can use the technique that we mentioned earlier to insert slide number in your powerpoint Slides, or even insert the numbers manually on every new slide. However, if you want to put the slide number in a different format, using XX of YY where YY is the total of Slides in your presentation, then we need to use something differently.
This is a free powerpoint add-in that allows a user to add the ‘Slide 4 of 12’ function to their presentations. It also contains a feature that allows user to save a selection of Slides as a new presentation.
Download free addin from http://billdilworth.mvps.org/PageXXofYY.htm