Unpicking the workings of a numerical trick allows students to put their algebra skills to use, says Colin Foster
To many KS4 students, algebra is morass of letters, numbers and symbols which have to be manipulated according to arbitrary and pointless rules to obtain a ‘correct answer’ which has no meaning or importance outside of the question. In this lesson, algebra is used to make sense of a number trick that the teacher performs. Students are asked to explore the mechanics, experiment with some numbers, and then use algebra to try to probe exactly how and why the trick works. It’s easy to check the rule on a few numerical examples by working them out, but a short piece of algebra helps students to see what is going on under the surface. This lesson provides an opportunity to work on expanding brackets and simplifying algebraic expressions, as well as making sense of the final answer in terms of the place value of the original numbers.
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