This answer finds the sum of one of each pair of faces (lb + bh + lh = 160 + 224 + 560 = 944) but forgets that a cuboid has 6 faces arranged in 3 identical pairs — the total must be multiplied by 2.
PRIMARY 4 · MATHEMATICS
Geometry
Top 5 mistakes
Ranked by how often they appear across 72 MOE-aligned practice questions in our archive.
This answer adds only the top/bottom faces and the two long side faces: 2(20 × 8) + 2(20 × 28) = 320 + 1120 = 1440. It leaves out the two short side faces (8 × 28), which are also part of the net.
This answer includes the two short side faces and the two long side faces: 2(8 × 28) + 2(20 × 28) = 448 + 1120 = 1568. It leaves out the two top and bottom faces (20 × 8), which are also part of the net.
Different views of a rectangular prism show different 2D shapes depending on the viewing angle.
The front view is not always a square; it depends on the prism's dimensions.
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