It’s type IS a very common math problem, and yes it’s middle-school level, or basic high school level. IIRC, it or something like it is always covered in Geometry and in math aptitude tests.
Its writing needs work, though:
* The wording “A stick that is 60 inches” is too short for a math problem. You should specify that’s how long it is.
* “parts that is” -> “parts that are”
* “smallest and the largest” -> “shortest and the longest”
* ” It does help to know what is meant by average and how it can be used.” – Does it? The problem itself doesn’t mention an average.
* “The problem also requires understanding the triangle inequality.” – No it does not.
* Like many basic geometry problems, it can be solved by logic if one understands arithmetic and knows what a triangle is. And that tends to involve more real understanding than invoking formally named theorems.
More importantly, to me: Like most math story problems, it tries to claim relevance to the real world by mentioning a real thing (the stick) and them immediately betrays that premise by failing to take it seriously at all.
That is, no you can’t break a stick into a super-tiny sliver, and call that part of a triangle. At the very least, there should be a line about what the shortest piece that can be broken off the stick is, and that you can’t break the stick at an angle to create sharp ends that total longer length than the original stick, which you totally could do with a real stick.
If you’re not going to take the stick seriously, don’t undermine everyone’s integrity by mentioning it – just talk about a theoretical triangle.