Some videos on permutation and combinations

https://www.youtube.com/watch?v=hJRXKq2GEo8&hd=1

https://www.youtube.com/watch?v=qaFNhwNBY3k&hd=1

A somewhat longer video

https://www.youtube.com/watch?v=QCq6qRJCTj8&hd=1 by Pushpinder Gill