Khan Academy offers good explanations about statistical questions, however, often a complex problem can't be easily answered in closed form solution.   A more often reliable way is to use simulation.  But that is perceived to be difficult.   However, using the free Excel tool SIPmath from www.probabilitymanagement.org solves that issue.   Simulation models are easily generated and can be shared with others without them having the SIPmath tool.   

An example is the birthday problem that Sal solves using factorials.   However, a much more complete answer is generated using simulation with SIPmath.   Contact me for a copy of the model.   Below are graphics of the complete answer.   

Please "up vote" this post if you agree that simulation is a good way to address questions.  Also please take a look at my YouTube channel that shows many applications of the free SIPmath tool.

                                 Brian Putt

                                 Brian@theputts.com