How many slide in PowerPoint can you work with at a time?
You can only really actually work with one at a time. However,
if you are using a Master Slide, you can affect all slides on your
presentation. You can also do things to some or all of your slides
in the Slide Sorter, like setting transitions. How many slides you
can have will depend on the amount of memory you have, but it is
not good design practice to have too many slides in a
presentation.