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HOW TO ACE THE
BRAINTEASER
INTERVIEW
JOHN KADOR
MCGRAW-HILL
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Copyright © 2005 by John Kador. All rights reserved. Manufactured in the United States of America. Except as permit-
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DOI: 10.1036/0071446060
(cid:2)
To Peter and Robert, my brothers
For more information about this title, click here.
CONTENTS
Preface v
Acknowledgments ix
To the Reader xi
Chapter 1 Riddle Me This 1
Chapter 2 Strategies for Solutions 7
Chapter 3 Real-World Reasoning Puzzles 13
Puzzles 1–42
Chapter 4 Reasoning Puzzles That Don’t Require Math 53
Puzzles 43–74
Chapter 5 Reasoning Puzzles That Require Math 91
Puzzles 75–100
Chapter 6 Probability Puzzles 123
Puzzles 101–111
Chapter 7 Puzzles for Programmers and Coders 139
Puzzles 112–119
Chapter 8 Business Cases 153
Puzzles 120–127
iii
CONTENTS
Chapter 9 Gross Order ofEstimation Problems 181
Puzzles 128–141
Chapter 10 Performance Puzzles 197
Puzzles 142–152
Appendix A: Facts You Should Know 211
Appendix B: 20 Think-on-Your-Feet Questions 213
Appendix C: Additional Fermi Problems 215
Appendix D: Puzzles Inappropriate for Job Interviews 219
Appendix E: Additional Sources and Links 225
List ofProblems 235
iv
PREFACE
Here’s a brainteaser for you.
Why do employers subject already nervous job candidates to brain-
teasers, puzzles, business cases, and other mind-benders? Do such
puzzles really help employers build teams of highly logical, curious,
successful, hard-working, motivated contributors who can be expected
to hit the ground running?
Hardly anyone believes that. There are no studies that give scientific
support to the notion that success at brainteasers and logic puzzles
predicts success at the job. So if employers know that, why do inter-
viewers persist in using valuable job interview time for this peculiar style
of interviewing?
Interviewers look to brainteasers to do one thing: to start a safe con-
versation that reveals how smart candidates are. Intelligence is seen as
a critical predictor of success on the job, and brainteasers allow inter-
viewers to get a measure of a candidate’s intelligence. “There is a strong
correlation between basic intelligence and success in software engi-
neering,” says Ole Eichorn, chief technical officer (CTO) of Aperio
Technologies in Vista, California. “Unfortunately the forces of political
correctness have taken away a key tool—employers can’t give intelli-
gence tests to candidates. In the meantime, puzzles are a decent proxy.
By giving candidates good puzzles you get a fair estimate of how smart
they are, and the discussion gives you some interaction with the candi-
date, too.”
With the downturn in the tech sectors, more and more people are chas-
ing fewer jobs. Interviewers are often faced with hundreds of résumés
for one position. When all these candidates seem exceptionally qualified
v
Copyright © 2005 by John Kador. Click here for terms of use
PREFACE
for the job, how is the interviewer to select? Using brainteasers and puzzles
makes sense at companies that focus recruitment efforts more on what
candidates might do in the future than on what they have done in the past.
These companies understand that in today’s fast-paced global business
world, specific skills are of limited use because technology changes so
quickly. What is really needed, interviewers believe, are curious, obser-
vant, quick-witted candidates who welcome new challenges, demonstrate
mental agility under stressful conditions, learn quickly, defend their
thinking, and demonstrate enthusiasm for impossible tasks.
It also doesn’t hurt that Microsoft, the most successful company of all
time, is known to add brainteasers to the mix of interview questions it
asks the thousands of super-bright candidates who come knocking at
its gates. No human resources director has ever been fired for aligning
his or her company’s hiring practices with Microsoft’s.
PUZZLES AND BRAINTEASERS IN ACTION
Joel Spolsky, president of New York–based Fog Creek Software, under-
stands that brainteasers or other challenges are a critical part of the inter-
view process because they help narrow the large number of “maybes” that
crowd any job search. “There are three types of people in the software
field,” notes Spolsky, who got his first job at Microsoft. “At one end of
the scale, there are the unwashed masses, lacking even the most basic
skills for the job.” They are easy to ferret out and eliminate, often just by
reviewing a résumé and asking two or three quick questions. At the other
extreme are the superstars who write compilers for fun. “And in the
middle, you have a large number of ‘maybes’who seem like they might
just be able to contribute something,” Spolsky adds.
At Fog Creek, brainteasers are used to identify candidates who not
only are smart, but who get things done. “Our goal is to hire people
with aptitude, not a particular skill set,” Spolsky says. “Smartis impor-
tant, but hard to define; gets things doneis crucial. In order to be able
to tell, you’re going to have to ask the right questions.”
The brainteaser challenge comes after Spolsky establishes rapport
with the candidate, asks about skills and projects, and poses some be-
havioral questions (“Tell me about a time when you faced a deadline
crunch . . .”). The first thing Spolksy looks for in a candidate is passion.
vi
PREFACE
After that, he gives the candidate an impossible gross-order estimation
question. “The idea is to ask a question that they have no possible way of
answering, just to see how they handle it,” he says. How many optometrists
are there in Seattle? How many tons does the Washington Monument
weigh? How many gas stations are in Los Angeles? More of these puzzles
can be found in Chapter 9.
“What an applicant knows gets him or her through the first interview,”
says Ed Milano, vice president of Marketing and Program Development
at Design Continuum, a product design consulting firm with offices in
Boston, Milan, and Seoul. By the time the applicant gets to Milano, apti-
tude and experience are not in question. For Milano to make a job offer,
he has to see how the applicant thinks under stressful conditions, the
environment that often describes life at a consultancy that assists clients
with make-or-break strategic design programs.
Ed Milano, like many recruiters, has often found that starting an inter-
view with a brainteaser is effective. Logic puzzles have a long tradition
in fast-moving high-tech companies where being quick on your feet is
an asset. As the rest of the world has embraced the attributes of the fast-
moving, ever-wired, start-up mentality of the high-tech computer company,
many recruiters are adopting the in-your-face style of interviewing
associated with technology-intensive start-ups. Some recruiters earnestly
believe that brainteasers are valid tools to gauge the creativity, intelli-
gence, passion, resourcefulness, etc., of candidates. Others are willing
to accept that puzzles are little more than interview stunts that may or
may not reveal aspects of the candidate’s character and may actually
alienate some candidates. In any case, brainteasers are here to stay.
A reasonable question readers often ask me is, “Given that this book
has now published these brainteasers and their solutions, why would any
interviewer ever use these brainteasers again?”
Let me give two answers. First, interviewers love candidates who
have prepared for interviews. They want you to prepare. The fact is,
there are literally hundreds of Web sites that discuss these puzzles,
sometimes with solutions, sometimes not. Besides, many of these brain-
teasers don’t have solutions. And of the puzzles that do, interviewers
understand, as you should, that reading the solutions to these puzzles is
no substitute for understanding them and being able to carry on an
vii
Description:he inside track on how to beat the "logic puzzle" job interview As if job interviews weren't nerve-wracking enough, many companies, in their pursuit of the brightest and best, have begun beleaguering applicants with tests of logic, creativity, and analytical abilities. Many firms have replaced tradi
