In the thumbnail pane on the left, right-click the slide you want to duplicate and select “Duplicate Slide”. This will insert a duplicate slide immediately after the original slide.

To duplicate multiple slides

Select the slides you want to duplicate by clicking the first one, holding Shift, and clicking the last one. Or Ctrl+click to select non-consecutive slides.
Right-click your selection and choose “Duplicate Slide”.

Other ways to duplicate

Copy (Ctrl+C) and paste (Ctrl+V) a slide. The duplicate will be inserted after the slide you paste it on.
Drag and drop a slide thumbnail within the presentation to duplicate it.
Use the keyboard shortcut Ctrl+D to duplicate the selected slide. Press it multiple times to create multiple duplicates.

When duplicating

By default, duplicated slides keep the same formatting and theme as the original.
You can choose to have them take on the destination slide’s formatting instead when pasting.

So in summary, duplicating slides in PowerPoint 2010 is easy – just right click and choose “Duplicate Slide”, use copy/paste, drag and drop, or the handy Ctrl+D shortcut. You can duplicate single or multiple slides this way.