Discussion
The length, breadth and height of a room are 12 m, 10 m and 9 m respectively. Find the combined area of its four walls and its ceiling.
Answer: B
The four walls form a band of height 9 m around the floor's perimeter, and the ceiling is a rectangle the same size as the floor.
\[ \text{four walls} = 2(l + b)h = 2(12 + 10) \times 9 = 2 \times 22 \times 9 = 396 \text{ m}^{2} \]
\[ \text{ceiling} = l \times b = 12 \times 10 = 120 \text{ m}^{2} \]
\[ \text{total} = 396 + 120 = 516 \text{ m}^{2} \]
The floor is excluded, so this is not the full surface area of the cuboid - that would be \( 396 + 240 = 636 \) m², which is offered as the first distractor.
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