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its an Object

I agree. This teaches nothing but frustration and how to waste time.

Please do not forget to use spoiler tag next time.

As for your question: I am by not means expert here but I'd say it is indeed a common practice.

is 's' a map or an object?

this tested nothing other than my ability to google search a formula

This is not true: "This Kata teaches you the very basics of method creation."
It asks you to learn what methods are and how to add them to a class which is above beginner level. The kata doesn't teach you anything, it requires you to know it.

This is not a sentence: "Two objects that return a one word name in response to the first letter of the first name and one for the first letter of the surname are already given."

No, it isn't. https://en.wikipedia.org/wiki/Century

@trashy_incel although you're right, the point "2000 is not the twentieth century." is still there.