Hi Kerry, thanks for sharing. I love the four 4s problem because it takes simple concepts/methods and requires students to apply them creatively. It’s also a great context for thinking about constraints.
I also have to mention that you can make 5 without the factorial:
((4 x 4) + 4)/4 …
… but the beauty of these problems is that they do not privilege individual methods (and I’m pretty sure factorial is needed for some of the larger numbers anyway :)).