The prompt was devised by Amanda Kirby (a secondary school mathematics teacher). It has been inspired by bar modelling, which has become more common in UK classrooms since the growth of interest in Singapore. As a tool, the bar model can be used to teach a variety of mathematical concepts from ratio to solving algebraic equations. However, Amanda does not take the conventional classroom approach of introducing a problem and then the tool with which to solve it. Instead, she has made the tool itself the starting point. In this way, students are expected to construct a conceptual understanding of the bar model, rather than simply accept it as part of a procedure that helps to get the correct answer. The inclusion of '100' invites students to link the bar models to percentages and multipliers used in percentage increase and decrease.
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