The last one is an area of maths called set maths/set theory (factorials being one of the things you might have met here before), though actually might be a way of doing recursion for this. Getting into spoiler territory for next week's efforts, or maybe hidden bonus round, you will probably be told to expand it to 1000 or 10000 or something silly.

I suppose my usual "not doing someone's homework for them" rule is in effect here so instead a video

A different test but should give you some approaches that will work for you (sum of a set minus another set and all that)

That series by the way is a great one and you will learn quite a bit if you watch it.
WaffleRaccoon likes this.
Jun 22, 2020