The prompt has the potential to cover a wide range of topics in the school curriculum, including the areas of polygons and the circle, fractions, Pythagoras' Theorem, trigonometry, similar shapes and use of formulae. It has led to open inquiries that combine student questioning with teacher instruction in a mutually supporting process.
The prompt was inspired by an idea on the MathArguments180 blog. During a series of 180 ideas for discussion in mathematics classrooms, number 89 (April 2014) featured different shaded shapes and asked "which is the closest to being threefifths shaded?"

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