Continuing this line of reasoning leads to the conclusion that the expected number of records in the list of observations is The probability is 1/3 that the third observation is higher than the first two, so the expected number of record rainfalls in three years is. The expected number of record years in the first two years of record-keeping is therefore. So there is a probability of that the second year was a record year. In the second year, the rain could equally likely have been more than, or less than, the rainfall of the first year. The first year was undoubtedly a record year. How many record-breaking falls of rain do you expect have taken place over that period? We assume that the rainfall figures are random, in the sense that the amount of rain in any one year has no influence on the rainfall in any subsequent year. Suppose we have a list of rainfall figures for a hundred years. How often are weather records broken? The harmonic series gives the answer. I have seen this problem set in more than one Mathematics Olympiad paper, and its solution, a pretty piece of reasoning, is worth describing. It is an interesting observation that, after, never again lands on a whole number. So creeps ever more slowly to infinity, increasing by smaller and smaller steps. If is used to denote the sum to terms of the harmonic series, then Oresme's argument shows that Whose sum can clearly be made as large as we please. He noted that if you replace the seriesĪnd bracket the terms as shown, then the latter series is just This surprising result was first proved by a mediaeval French mathematician, Nichole Oresme, who lived over 600 years ago. However, the harmonic series actually diverges - the sum increases without bound. Such a calculator would tell you that the sum of the harmonic series is about 230, if you let it run long enough. That is because your typical calculator handles numbers only up to a certain size Indeed, if you asked your friendly pocket calculator or home computer to sum the series, you would get a finite sum. You might be excused for thinking that the sum to infinity of the harmonic series is some finite number, because as you add more and more terms, less and less is added to the running total. Nevertheless, we can answer the question: What is the sum "to infinity" of the harmonic series? There is no simple formula, akin to the formulae for the sums of arithmetic and geometric series, for the sum The problem of finding all harmonic bodies requires a knowledge of Euler's formula for polyhedra and Pell's equation for its solution. Simple enough question, but I've not seen it asked before. Are there any other "harmonic" bodies? There is the octahedron, with 8 faces, 12 edges and 6 vertices. Since 6, 8 and 12 are in harmonic progression, to Pythagoras the cube was a "harmonic" body. He noted, for example, that a cube has 6 faces, 8 vertices, and 12 edges. Pythagoras mixed his mathematics and physics with a liberal helping of mystical mumbo-jumbo.
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