Count regions A and B, then subtract their shared cubes only once. The stack does not fall or settle.
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First lesson in this subject: Turn a shape, don’t flip it
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Name each removal before counting. Add their sizes, subtract their overlap, then remove that union from the original total.
Count regions A and B, then subtract their shared cubes only once. The stack does not fall or settle.
Region A: Layer 2 Region B: Column x 1, y 2 Shared cubes
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First lesson in this subject: Turn a shape, don’t flip it
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Practice · Count hidden supporting cubes, or work out how many remain after removing a layer or column.
Book · Follow shapes through turns, folds, reflections, and different points of view.
Previous lesson · Check each cube’s neighbours, exclude the ground, and count cubes with the requested number of painted faces.
Next lesson · Learn the six face letters, and what a prime mark and a 2 change.
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