Art of Problem Solving: With or Without Replacement

Art of Problem Solving's Richard Rusczyk explains the difference between "with replacement" and "without replacement" in counting problems.

[tianwenhong]

11x10x9x8x7 is not a factorial and not all of them are but some other combos can be made into factorials.

[rit]

I found one it’s P(6, 3) which is 120 and 5! Is 120.

[michelefranzoni]

Does anyone know something about the question Richard makes at the end of the video? I'm stuck.

[rodidy]

My math professor made this so complicated, thank you so much for clarifying -___-

[parthagrawal]

I wonder why they named it the Liar's Club...
Thanks Richard for making my math life so much easier!