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.
For more KS4 maths lesson plans from Colin Foster click here.
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