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A good answer is something that gets you to the right order of magnitude that would be absolutely correct if your assumptions are correct. For example, the number of piano tuners in New York: So there are eight million people in NYC. Let's say that each household is two people, on average. So four million households. Because NYC is crowded, not many people have pianos in their homes -- let's say one in fifty. So 80,000 pianos. Let's double that to account for the schools and concert halls, so 160,000 pianos. On average, let's say a piano is tuned once every other year. So each year, there are 80,000 tunings. A piano has 88 strings, and let's say a trained tuner could tune about two per minute, so a piano takes forty-five minutes to tune. If the piano tuner knows where he's going, and makes appointments accordingly, let's say it takes another forty-five minutes to get from one appointment to the next. So ninety minutes is one piano tuning. One tuner works 50 weeks a year, 40 hours a week, so 2000 hours, or 1333 tunings. So 80,000 tunings / 1333 tunings per tuner = 60 tuners in NYC. Of course, that assumes each tuner works full-time. If we assume there are part-time tuners, that number only goes up. I'd round to 100. You see, the point isn't to get the exact number; the point is to show that you can figure out impossible problems. |