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Comment by aswanson | Hacker News Reader

I've never done a trade in my life and it took all of about 12 seconds to get the right answers on the first two. They didn't list the third. Seriously, 5.4 MM for that?...http://www.bloomberg.com/apps/news?pid=20601087&sid=a4iG...

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Here's a forum with the type of questions that more likely to be asked. These questions are more difficult. http://www.wilmott.com/categories.cfm?catid=26:

Example brainteaser:

"Last night I sat behind two wizards on a bus, and overheard the following:

A: I have a positive integral number of children, whose ages are positive integers, the sum of which is the number of this bus, while the product is my own age. B: How interesting! Perhaps if you told me your age and the number of your children, I could work out their individual ages? A: No. B: Aha! AT LAST I know how old you are!

Now what was the number of the bus?"

Discussion: http://www.wilmott.com/messageview.cfm?catid=26&threadid...

Wow, I read through the discussion. No way in hell anyone would be able to answer that in an interview, unless they'd seen it before.

It's definitely answerable in an interview situation. Some people should be able to answer it, no problemo, in a minute or two.

I don't think you understand the problem. Even if you manage to find 4, 4, 3, 1 and 6, 2, 2, 2, you still have to verify that if the sum is 12, then there is only 1 possible product. You'll note that nobody in the linked thread succeeds at this (one guy proves that 12 works by exhaustive search, not really a possibility in an interview...)

Well, I saw it before, and it took a several minutes then, maybe 5 or 15, I don't really remember. Then you have to consider that companies like D.E. Shaw end up hiring people who would end up giggling at how long somebody slow like me would take to solve the problem.

it's also a Slate article vs. HN. i'd expect them to post questions that dazzle the least common denominator, while still allowing them to understand what's going on after a brief explanation. i'd be worried if HN _couldn't_ solve problems understandable by Slate's target audience.

Um, can someone explain the answer to the first question? Why wouldn't it go lower than the low eighties? Or higher, for that matter? How would the price change if there were 1000 sellers?

Basically the sellers end up bidding for the opportunity to sell. So basically some sellers won't be willing to sell below 89, more won't be willing to sell below 88, and even more won't be willing to sell be 87. And it works the other way too, so the lower the price gets, the more people are willing to buy. So theoretically, when the number of buyers equals the number of sellers, transactions end up occurring. This is assuming that the market is efficient, which isn't always the case.

If there were 1000 sellers, the price would drop even lower, because there is more competition among the sellers.

By this reasoning, equally valid answers would be $0.01 and $90.99.

The point of the question is that there is no mathematically "right" answer. The interviewer knows the answer from experience, and (s)he's testing two things: whether the interviewee's intuition on the market is right, and, if not, how well the interviewee takes to being corrected.

Your answers are "right", in that they are possible, but they are not the numbers the interview wants to hear.

That makes more sense. I thought there was some obvious game theory principle I was missing, since somebody commented that they could answer the question without knowing anything about trading.

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