The Interview Brainteaser and its Discontents - 3

by Joe Mabel

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(This is the continuation of an article about the use and abuse of brainteasers in job interviews.)

(Horror) stories

On the following pages are a few stories that illustrate how badly the use of brainteasers in interviews can go wrong. After discussions with numerous colleagues, my belief is that they are not isolated incidents, but are reasonably representative of a widespread problem. I'm not going to say exactly what companies were involved, but all examples are drawn from the software industry, and all of these are cases of people interviewing either for management or senior technical positions. These are not all from my personal experience, but I was, indeed, the candidate in the Pirate story: that incident was the genesis of this article.

Each story illustrates at least a few of the points above. I'm afraid I don't have a good story to demonstrate the liar/sociopath scenario, because who would tell me? Nonetheless, a more cynical friend of mine has provided a pretty good reconstruction of how it would work.

Naturally, I've had to approximate the way each problem was framed and what interactions followed, but the salient points are drawn from life. Since I have all the stories from the point of view of the interviewee, I cannot speak for the intentions of the people who posed the questions. All three said to the respective candidates, I want to see how you think. It is possible that one or another interviewer deliberately posed an incorrectly or incompletely specified problem; if so, they never 'fessed up to the candidate.

Brainteaser 1: Bear Hunting

The problem as posed: A man is out hunting. He walks one mile south. He makes a ninety degree turn to his left. He walks another mile. He makes another ninety degree turn to his left and walks another mile. He is now back where he first started. He shoots a bear. What color is the bear?

Brainteaser 2: Spinning Wheel

The problem as posed: A wheel is painted half black and half white. You can place two stationary sensors anywhere on the surface of the wheel. The sensors tell you what color they see. How can you tell which way the wheel is spinning? And how long does it take before you know?

Brainteaser 3: A Pirate as Emissary

The problem as posed: There are two kings, each on an island. Each king has one valuable diamond, one box, one lock, and one key. The king on the first island has a daughter (so we'll call him the Daughter King). The king on the second island has a son (so we'll call him the Son King).

The only way between the islands is a pirate ship. The pirate is open to doing a bit of commerce, but he's a pirate. If he can get the diamond and keep it, he will. The kings, on the other hand, are honest, which is to say that they don't steal and they keep their word.

The kings are trying to arrange a marriage between their respective offspring. The diamond is what proves how great a king is. The Son King has demanded to see the diamond belonging to the Daughter King. The Daughter King is willing to show it to him. How can he show off his diamond (and get it back) without any possibility of its being stolen?

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Originally written: June 26, 2002
Article copyright © 2002 Joseph L. Mabel
All rights reserved.
Copyleft: With appropriate notification and appropriate credit, non-commercial reproduction is welcome: contact me if you have any desire to reproduce these materials in whole or in part.

Last modified: 26 June 2002

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