How can all of these estimates produce a reasonable answer?

Now, I know what you must be thinking: How can all of these estimates produce a reasonable answer?Well, it's rather simple.In any Fermi problem, it is assumed that the overestimates and underestimates balance each other out,and produce an estimation that is usually within one order of magnitude of the actual answer.In our case we can confirm this by looking in the phone book for the number of piano tuners listed in Chicago.What do we find? Pretty incredible, given our order-of-magnitude estimation.But, hey - that's the power of 10.