The same problem here. It takes 20 minutes to find out what's wrong.

description reworded a bit.

I still do not understand. From what I understand of the description, the taxes exceed the interest, so he would be losing money.

"Behavior" Is triggering me as a non-American being taught English. We write it with an extra 'u': "Behaviour"; in fact, I believe the whole world does except you guys...

Nonetheless, a very good step towards Composition. Could use some more refinement, but as a step-in it's pretty good.

If one wants to learn more about Composition, I recommend looking at https://en.wikipedia.org/wiki/Composition_over_inheritance

Holy shit does one need to read really well to not have to resort to searching the web how taxes work (I, for one, have never done taxes, always phoned the tax office and had a lady explain it to me. At which point I instantly forgot as soon as I hung up).
Maybe a more.. "clear" formula would be handy? But then you'd sell the answer in the description...
Though one indeed. Enjoyed it.

"Whoever thought this was a good Kata for 8 kyu (Seen as kata ranks aren't defined by the author.) didn't think things through.
Mathematical questions and tricks on this level don't belong in 8 kyu. 8 Kyu is meant for simple problem solving, fundamentals and general trainign on the lowest level."

Is what I see mentioned the most. But what it comes down to is reading and understanding the question. This is something often missed in (general) communication between project-members.
I could argue, however, that a problem like this is better suited for situations like teacher-student in a class room as a joke.

Just now saw your reply. Actually saved me in checking for cases the other day. Unfortunately saw this too late... <3

char has .ToUpperInvariant() and .ToLowerInvariant() which are better optimized in cases like this. Worth taking a look at if you're interested.