How many piano tuners are there in Chicago?

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Superforecasting: The Art and Science of Prediction by Philip Tetlock, Dan Gardner

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Now I’ll assemble my guesses to make a final calculation: If 50,000 pianos need tuning once a year, and it takes 2 hours to tune one piano, that’s 100,000 total piano-tuning hours. Divide that by the annual number of hours worked by one piano tuner and you get 62.5 piano tuners in Chicago. So I will estimate that there are sixty-three piano tuners in Chicago. How close am I? Many people have taken a crack at Fermi’s classic puzzler over the years, including the psychologist Daniel Levitin, whose presentation I’ve adapted here.6 Levitin found eighty-three listings for piano tuners in the Chicago yellow pages, but many were duplicates, such as businesses with more than one phone number. So the precise number isn’t certain. But my estimate, which rests on a lot of crude guesswork, looks suprisingly close to the mark.

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In fact, no serious analysis of this critical forecast was conducted until 1967—years after the decisions to escalate had been made.4 “The foundations of our decision making were gravely flawed,” McNamara wrote in his autobiography. “We failed to analyze our assumptions critically, then or later.”5 Ultimately, it’s not the crunching power that counts. It’s how you use it. Fermi-ize Here’s a question that definitely was not asked in the forecasting tournament: How many piano tuners are there in Chicago? Don’t even think about letting Google find the answer for you. The Italian American physicist Enrico Fermi—a central figure in the invention of the atomic bomb—concocted this little brainteaser decades before the invention of the Internet. And Fermi’s students did not have the Chicago yellow pages at hand.

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Fermi knew people could do much better and the key was to break down the question with more questions like “What would have to be true for this to happen?” Here, we can break the question down by asking, “What information would allow me to answer the question?” So what would we need to know to calculate the number of piano tuners in Chicago? Well, the number of piano tuners depends on how much piano-tuning work there is and how much work it takes to employ one piano tuner. So I could nail this question if I knew four facts: 1. The number of pianos in Chicago 2. How often pianos are tuned each year 3. How long it takes to tune a piano 4.

The Organized Mind: Thinking Straight in the Age of Information Overload by Daniel J. Levitin

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“How many Reese’s Peanut Butter Cups would it take to encircle the globe at the equator?” and “How many piano tuners are there in Chicago?” Approximating involves making a series of educated guesses systematically by partitioning the problem into manageable chunks, identifying assumptions, and then using your general knowledge of the world to fill in the blanks. How would you solve the problem of “How many piano tuners are there in Chicago?” Google wants to know how people make sense of the problem—how they divide up the knowns and unknowns systematically. Remember, you can’t simply call the Piano Tuners Union of Chicago and ask; you have to work this from facts (or reasonable guesses) that you can pull out of your head.

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In one year, a piano tuner can tune 1,000 pianos (2,000 hours per year ÷ 2 hours per piano). It would take 50 tuners to tune 50,000 pianos (50,000 pianos ÷ 1,000 pianos tuned by each piano tuner). Add 15% to that number to account for travel time, meaning that there are approximately 58 piano tuners in Chicago. What is the real answer? The Yellow Pages for Chicago lists 83. This includes some duplicates (businesses with more than one phone number are listed twice), and the category includes piano and organ technicians who are not tuners. Deduct 25 for these anomalies, and an estimate of 58 appears to be very close.

Stealing Fire: How Silicon Valley, the Navy SEALs, and Maverick Scientists Are Revolutionizing the Way We Live and Work by Steven Kotler, Jamie Wheal

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These days, they’ll just get trolled online, then ignored. And what that does is leave more room for open experimentation. It disempowers anyone tempted to escalate his position and privilege, and empowers everyone else to make sense of their own experiences. When the physicist Enrico Fermi famously guessed the number of piano tuners in Chicago, or the number of stars in our galaxy, he did so by applying provisional estimates to impossibly large problems. And while never exact, his guesses often landed within an order of magnitude of the actual number—enough, in other words, to act upon. Today we’re following Fermi’s lead, applying the power of Big Data to approximate answers to the Big Questions.

Chaos Monkeys: Obscene Fortune and Random Failure in Silicon Valley by Antonio Garcia Martinez

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Next up was Rohit Dhawan. Another Googler, he had that very well put together and confident air of someone who felt he had mastered his field of work (he was a Penn grad, of course). His angle was analytical ability, and he asked me a variant of that legendary Enrico Fermi brainteaser about piano tuners in Chicago. His variant was to estimate the number of planes in the sky at any given moment. It required nothing more than some rough base assumptions about number of airports and flights per day, and then some dimensional analysis that got us within an order of magnitude of reality, and we were done in ten minutes.

Are You Smart Enough to Work at Google?: Trick Questions, Zen-Like Riddles, Insanely Difficult Puzzles, and Other Devious Interviewing Techniques You ... Know to Get a Job Anywhere in the New Economy by William Poundstone

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He spent much of his lunch calculating how many extraterrestrial civilizations there were in the universe and how close the nearest one would be. This was the classic “Fermi question.” Back at the University of Chicago, Fermi tormented his students with only somewhat easier questions. His most famous classroom riddle was, “How many piano tuners are there in Chicago?” Fermi staunchly believed that anyone with a PhD in physics should be able to estimate just about anything. Somewhere along the line the “PhD in physics” part got dropped. Today’s employers have gotten the idea that everyone, including humanities majors, should be able to estimate odd quantities on a job interview.

The Greatest Story Ever Told--So Far by Lawrence M. Krauss

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He refined his abilities and helped his students do so by inventing what we now call Fermi Problems, which he is also said to have assigned at lunchtime each day to the team working for him. My favorite problem, which I always assign to my introductory-physics students, is “How many piano tuners are there in Chicago?” Try it. If you get between one hundred and five hundred, you did well. Fermi won the Nobel Prize for his experimental work, but his theoretical legacy for physics may be far greater. True to form, the “theory” he proposed in his famously rejected paper on neutron decay was remarkably simple, yet it did the job.

Working: People Talk About What They Do All Day and How They Feel About What They Do by Studs Terkel

activist lawyer, business cycle, call centre, card file, cuban missile crisis, Ford Model T, Ford paid five dollars a day, half of the world's population has never made a phone call, How many piano tuners are there in Chicago?, job satisfaction, planned obsolescence, Ralph Nader, strikebreaker, traveling salesman, urban renewal, War on Poverty, working poor, Yogi Berra, zero day

Thinking in Numbers by Daniel Tammet

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