Zero. Zilch. Nothing. Absolutely sod all.
From the OP's original post, after seeing the questions over the days, his claim:
If you can't answer the majority of the questions on these four papers, and you're working or intend to work as a software developer, you should ask yourself why — most likely you're either you're missing something you really should know, or you're lucky enough to be working within a narrow area where your deficit doesn't matter
So far almost none of the questions on any of the days have been the slightest bit 'important' in software development.
I don't have all of his questions at hand, but from memory:
1. Basic knowledge of statistics and probability is required for machine learning.
2. His question about zeroing multi-dimension array is to test if you understand the under lying memory model.
3. Do we really need to discuss why you should know how cryptographic hashes work?
4. B-tree has better locality of reference and are de-facto data structure for storage for majority of the cases. Granted, not many people do low level storage, but does that somehow makes it irrelevant to software development?
5. Mutex, rw-locks etc are building blocks of concurrent programs.
I don't know why you are assuming anything which isn't CRUD web development doesn't have anything to do with software development.
I know Coursera has released bits of this sort of coursework, but I don't think they've put it in a guided, ordered curriculum form with preqs.
If someone puts this together, I'll gladly pay for it.
I think the guide to asking questions on Math, Algorithms and Data structures is to ask real world problems which will require you to use these problems.
Its like Math Vs Physics. You can learn the pure math there is out there, but unless you start studying physics you don't quite see how those concepts are applicable to the real world.
Similarly, its simple to ask these questions to a programmer. Give him a real world programming problem to solve, and then see how he uses the concepts from math and CS to solve them.
Naive bayes, with a relevant dataset, does a very fine job of data classification(sentiment analysis, spam detection...). Also, almost everyone who isn't a liberal arts major would have come across Bayes theorem in high school or college.
The question about A/B testing is solving simple linear equations. I believe anyone in 10th grade or above should be able to solve it.
Hashing and MAC are pretty much application level security - they don't require intrinsic knowledge of how; what and why is something an application developer should know.
That leaves us with that harmonic progression thingy and padding. Padding, I think, is to avoid cryptanalysis(extrapolating from what you know is a part of knowing things:)).
Overall, I won't say he is going overboard with his questions. If anything, to anyone familiar with the topics, his questions are pretty trivial. The only thing under contention is if the topics he considers relevant are actually relevant.