Here is a set of free short videos for stepwise preparation of Permutations & Combinations on GMAT. For a more detailed treatment of the topic, you may want to opt for our GMAT online course or our GMAT test series of 15 mock tests.
A Basic Approach Towards Counting the Arrangements
Difference Between "Permutations" and "Combinations"
Permutations and Combinations Formula
Applying the Permutations and Combinations Formula
Relationship Between Permutations and Combinations
An Explanatory Permutations Example
An Explanatory Combinations Example