In The Number Devil by Hans Magnus Enzensberger, Robert, a boy who hates math, is visited in his dreams by a number devil. The number devil is a bit annoying in the beginning but becomes a likeable character by the end of the book. Robert is not sure he likes the number devil visiting his dreams, but even dreams of math are better than his normal bad dreams and eventually he looks forward to his encounters with the number devil.
From the beginning the number devil insists on the difference between calculation and mathematics. Learning to add/subtract/multiply/divide is important but not interesting, while mathematics is beautiful art, interesting puzzles, and amazing patterns. Through a series of dream encounters Robert learns about infinity, the importance of zero, square numbers, triangular numbers, Fibonacci numbers, Pascal’s triangle, combinations and permutations and more. I love that the interrelationship of these concepts are explored also and the reader is invited to continue exploring on her own. In some of the concepts the author uses made up terms like rutabaga for square root and unreasonable numbers for irrational numbers. He explains at the end of the book that technical terms don’t belong in dreams and provides a list of the actual names of the concepts. This contributes to the author’s premise that math is to be played with but does require that the appropriate terminology be introduced as I’m not sure a student would read the glossary to learn the correct terms. I would have prefered the correct terms be used in the book but can see how using rutabaga for square root encourages playfulness.
Describing the process of mathematical proof is one of the strengths of this book. As Robert learns more and thinks more he wants to know the ‘whys’ and ‘hows’ of the tricks and patterns the number devil has showed him. The number devil agrees that examples can only go so far in learning mathematics, you need to prove an idea before you can be convinced it is true. The proof process is described as a raging stream that you must cross by leaping from rock to rock. The rocks are the axioms and theorems that have already been proved. To cross the stream you may have to try several different paths as one that looks promising from the bank turns out to be a dead-end. What a wonderful way to illustrate the adventure of proof while giving encouragement to experiment and explore!
In the end Robert realizes that he enjoys math, not because the number devil has made it easy, but because he has discovered that math is interesting and full of surprising relationships. Most importantly, Robert is no longer scared of math but excited about all there is to discover and learn.
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