using factorial in probability question

[resolved]

"Meanwhile, being aware of how the machine works internally should help avoid unexpected results."

Not to be facetious -- but what resources are available to me to understand the internal working of the HP Prime -- what is it that I "should" know to be able to intelligently use this machine???? -- if it is for me to believe that such knowledge is simply compiled, available and understandable to the average high school / college student, appears ludicrous, then expecting the casual user to know that overflow errors are hidden from them is also ludicrous. How many HP Prime users, off the top of their head could tell you at what factorial the HP Prime hits its upper limit -- none unless they researched it.

The original question I asked was a simple high school statistics problem, which millions of students must study. You don't truly believe they must understand the internal working of the HP Prime before they can do such elementary math????

This is not a judgment of you Joe --- You have been more than helpful and inspiring, but it is a judgment on HP not to be more informative, it almost seems sadistic to set up casual users to such failures.......

Understand that I truly love this machine, I can actually read the screen without fighting the room's light source, but it can still be improved....