Why Are Manhole Covers Round? (And How to Deal With Other Trick Interview Questions.) Companies of all stripes are zinging job applicants with sadistic puzzlers. There are no right answers. But there is a right way to answer.
By William Poundstone

(Business 2.0) – Sometime after "Tell us about yourself" and "Describe a challenge you faced at your current job" comes the zinger, that off-the-wall Zen riddler that can leave you sputtering in the middle of a job interview: Why are Coke cans tapered? How would you weigh the world's fattest man without using a scale? How many tennis balls are in the air in New Zealand right now? It's a growing trend in this buyer's market for the best and brightest--everyone from tech companies like Microsoft and Hewlett-Packard to Wall Street investment banks to the U.S. military uses these sorts of questions to gauge a candidate's problem-solving ability.

Tough? Sure. Sadistic? Perhaps. Unanswerable? Hardly. In the spirit of full disclosure, you should know that I've recently written a book, How Would You Move Mount Fuji?, that examines Microsoft's use of such questions and provides a host of possible answers. But there are always new questions, and in any case, the interviewers aren't actually looking for the "right" answer. They want to see how you think. So, as much as I'd like you to spring for the book, here instead are a few tips for wrestling any zinger into submission.

Accept that whatever you think of first will be wrong.

The answer that immediately pops into your head is almost never right. If it were, this wouldn't be much of a puzzle.

A better approach is to start your running narration immediately. Introduce the first idea you think of with a note of skepticism: "Well, the obvious solution would be...." Then examine exactly why it fails, and work out your answer aloud. This not only fills the dead air while you take some time to think, but also shows the interviewer how you approach a problem.

Memorize a few key figures.

The most feared types of questions ask for information you couldn't possibly know: How many piano tuners are there in the world? How many Ping-Pong balls can you stuff into a 747? Rest assured: The interviewer doesn't know the answer either. Nor does he much care. The hidden agenda is to see how well you can outline a logical procedure for estimating the answer. Accuracy doesn't count--much.

Still, it can't hurt to brush up on your algebra and geometry--basic tools for working out these sorts of problems. And you should have a rough idea of the population of the world (6.3 billion), the United States (290 million), and the city where you're interviewing. Those figures determine the size of markets, no matter what business you're in. In contrast, it's not nearly so damaging to have no clue about the length of a 747 (unless you're interviewing at Boeing; in that case, it's 231 feet).

Give an answer that hasn't been heard before.

When a question has more than one "good" answer, you can gain points for novelty. Joel Spolsky, a former Microsoft program manager, once asked job seekers to design a spice rack for blind people. One described a counter-level drawer that alleviated the need to feel for a wall-hung rack. This ergonomic issue hadn't occurred to any other candidate; Spolsky hired him on the strength of that answer alone. "He went on to be one of the best program managers," Spolsky says.

If the question is brief, your answer shouldn't be.

Puzzles like "Why do mirrors reverse right and left but not top and bottom?" often call for long, involved responses. Be sure to include all the logic behind your reasoning, since you may be penalized for leaving out an important part of the answer. If, however, the challenge is vague or open to interpretation--"Create the perfect car for Bill Gates"--fire off some questions of your own: You are expected to ask for more information. Just don't get upset and ask the interviewer whether it's possible for him to assume a certain anatomically challenging position. --WILLIAM POUNDSTONE