I just watched and Khan Academy's videos on permutations and combinations. Though they were good, (I mean better than most other online resources) they were just not enough. Sal tries much to make us understand, but we fail to understand what is going on *in his head* If we could understand that we'd have the same level of understanding of the topic as Sal. I mean you need to make better videos on permutations and combinations which should provide a greater level of clarity and intuition and help us to visualise what is going on. I think you would have to do it in the Ted Ed style. The blackboard style does not work everywhere.