Unit 25
The Art of Smart Guessing
Several days ago, interviewing job candidates, I grew tired of asking "What experience do you have?" I decided on a quiz to find out how resourceful a thinker the new hire might be. Here it is: You are on a yacht sailing the Pacific Ocean. Your navigator announces you are over the deepest point, the Mariana Trench. Just then, a clumsy guest accidentally drops a 12-pound cannonball over the side. How long will it take for the cannonball to reach the bottom of the ocean?
Before reading on, try to solve this yourself -- paying special attention to how you might solve it. Did you make a completely wild guess because "there wasn't enough information?" Did you get too bogged down in the details trying to come up with the "exactly right" answer? Or did you zero in on the two most important problems -- how deep is the Mariana Trench and how fast might a cannonball fall through the water? Most of my candidates simply made a wild guess. Rarely was someone willing to risk an approximation.
What does this have to do with business or creativity? A great deal. In the real world, we frequently need to make decisions when the full information does not exist. A problem that doesn't contain all the information deeded to solve it is called a Fermi problem, named after Nobel Prize-winning physicist Enrico Fermi.
Fermi once asked is students how many piano tuners there were in Chicago. To answer the question, he recommended breaking it down into smaller, more manageable questions. How many people live in Chicago? Three million would be a reasonable estimate. How many people per family? Assume an average of four. How many families own pianos? Say one out of three. Then there are about 250,000 pianos in Chicago. How often would each be tuned? Maybe once every five years. That makes 50,000 tunings a year. How many pianos can one tuner tune in a day? Four? And how many in a year? Assuming 250 working days, one tuner can handle 1,000 pianos a year. So there's work for approximately 50 piano tuners in Chicago -- which, as it turns out, is reasonably close to the actual number in the Yellow Pages.
Why was guesswork so accurate? The law of averages is partly responsible. At any point, your assumptions may be too high or too low. But because of the law of averages, your mistakes will frequently balance out.
By the way, the Mariana Trench is about six nautical miles deep, and a cannonball drops at a rate of ten feet per second. So it took the cannonball about an hour to reach the bottom. Could this be guess? If you know Earth's highest point Mount Everest, is 29,000 feet, you might reasonably conclude that its lowest point would be close to the same distance. Then you might imagine that a heavy object would take one second to fall through the water of a 10-foot-deep swimming pool. These estimates would bring you close enough to the correct answer. |