MATHEMATICAL THINKING IS IMPORTANT AS A WAY OF LEARNING MATHEMATICS In this section, I will illustrate these four processes of mathematical thinking in the context of a problem that may be used to stimulate mathematical thinking about numbers or as an introduction to algebra. If students’ ability to think mathematically is an important outcome of schooling, then it is clear that mathematical thinking must feature prominently in lessons. Number puzzles and tricks are excellent for these purposes, and in the presentation I will use a number puzzle in a format of the Flash Mind Reader, created by Andy
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Naughton and published on the internet (HREF1). The Flash Mind Reader does not look like a number puzzle. Indeed its creator writes: We have been asked many times how the Mind Reader works, but will not publish that information on this website. All magicians […] do not give away how their effects work. The reason for this is that it spoils the fun for those who like to remain mystified and when you do find out how something works it's always a bit of a let-down. If you are really keen to find out how it works we suggest that you apply your brain and try to work it out on paper or search further afield. (HREF1) As with many other number tricks, an audience member secretly chooses a number (and a symbol), a mathematical process is carried out, and the computer reveals the audience member’s choice. In this case, a number is chosen, the sum of the digits is subtracted from the number and a symbol corresponding to this number is found from a table. The computer then magically shows the right symbol. The Flash Mind Reader is too difficult to use in most elementary school classes, the target of this conference, but I have selected it so that my audience of mathematics education experts can experience afresh some of the magic and mystery of numbers. As the group works towards a solution, we have many opportunities to observe mathematical thinking in action. Through this process of shared problem solving as we investigate the Flash Mind Reader, I hope to make the following points about mathematical thinking. Firstly, when people first see the Flash Mind Reader, mathematical explanations are far from their minds. Some people propose that it really does read minds, and they may try to test their theory by not concentrating hard on the number that they choose. Others hypothesise that the program exerts some psychological power over the person’s choice of number. Others suggest it is only an optical illusion, resulting from staring at the screen. This illustrates that a key component of mathematical thinking is having a disposition to looking at the world in a mathematical way, and an attitude of seeking a logical explanation. As we seek to explain how the Flash Mind reader works, the fundamental processes of thinking mathematically will be evident. The most basic way of trying to understand a problem situation is to try the Flash Mind Reader several times, with different numbers and different types of numbers. This helps us understand the problem (in this case, what is to be explained) and to gather some information. This is a simple example of specialising, the first of the four processes of thinking mathematically processes. As we enter more deeply into the problem, specialising changes its character. First we may look at one number, noting that if 87 is the number, then the sum of its digits is 15 and 87 – 15 is 72. Beginning to work systematically leads to evidence of a pattern:
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87 8 + 7 = 15 87 – 15 = 72 86 8 + 6 = 14 86 – 14 = 72 85 8 + 5 = 13 85 – 13 = 72 84 8 + 4 = 12 84 – 12 = 72 and a cycle of experimentation (which numbers lead to 72?, what do other numbers lead to?) and generalising follows. Of course, at this stage it is important to note the value of working with the unclosed expressions such as 8+7 instead of the closed 15, because this reveals the general patterns and reasons so much better. Working with the unclosed expression to reveal structure is an admirable feature of Japanese elementary education. 87 87 – 7 = 80 80 – 8 = 72 86 86 – 6 = 80 80 – 8 = 72 85 85 – 5 = 80 80 – 8 = 72 84 84 – 4 = 80 80 – 8 = 72 It is also worthwhile noting at this point, that although we are working with a specific example, the aim here is to see the general in the specific. This generalising may lead to a conjecture that the trick works because all starting numbers produce a multiple of 9 and all multiples of 9 have the same symbol. But this conjecture is not quite true and further examination of examples (more specialising) finally identifies the exceptions and leads to a convincing argument. In school, we aim for students to be able to use algebra to write a proof, but even before they have this skill, they can be produce convincing arguments. An orientation to justify and prove (at an appropriate level of formality) is important throughout school. If students are to become good mathematical thinkers, then mathematical thinking needs to be a prominent part of their education. In addition, however, students who have an understanding of the components of mathematical thinking will be able to use these abilities independently to make sense of mathematics that they are learning. For example, if they do not understand what a question is asking, they should decide themselves to try an example (specialise) to see what happens, and if they are oriented to constructing convincing arguments, then they can learn from reasons rather than rules. Experiences like the exploration above, at an appropriate level build these dispositions.