Khan Academy (English - US curriculum)
Math by grade
Eureka Math/EngageNY
Precalculus (Eureka Math/EngageNY)
Module 5: Probability and statistics
Topic A: Lesson 2: Counting rules—The fundamental counting principle and permutations
Zero factorial or 0!
Zero factorial or 0!
Sal explains the intuition behind zero factorial.
License: CC BY-NC-SA by Khan Academy