I love this solution

He's right, read the other note:

Don't forget to convert the percent parameter as a percentage in the body of your function: if the parameter percent is 2 you have to convert it to 0.02.

Very naive of you not to read instructions.

"There are no fractions of people. At the end of each year, the population count is an integer: 252.8 people round down to 252 persons."

You could say the same about any language

Coding in C# is like coding a suit, everything looks neat and tidy if you follow the conventions and standards. Otherwise your code will look like a fat cat.

Pretty, kind of clever, but not the cleverest nor very performant. Why iterate twice when you can have a single for loop?

A detailed comment isn't necessary, just some mild familiarity with Linq and the string constructor.

C# is not a good code golf language

Instead of one run in search of the maximum and minimum , it is run twice here.

Really clever, but a bit hard to read. A few line breaks and spaces and it would be better. For performance of course not the best solution but from effort.

I like how peoples solving problems in one line thinking its a good practice, this is a nightmare for maintenance if you asked me, and this line is totally NOT CLEAR, a very detailed comments is required to understand whats going on in there for someone who doesn't know the context .

Because sorting the array once is slower than iterating through it twice.

Why not sort the array once and then take the last and first elements?