Discussion

If a rectangular cuboid is 15 cm long, 10 cm wide and 9 cm high, then the total surface area of the cuboid is

Answer: A

A cuboid's total surface area sums its three pairs of faces.

\[ \text{TSA} = 2(lb + bh + hl) \]

\[ = 2(15 \times 10 + 10 \times 9 + 9 \times 15) \]

\[ = 2(150 + 90 + 135) = 2(375) = 750 \text{ cm}^{2} \]

Each product must be counted twice, once for each of the opposite faces - the single sum of 375 is exactly half the answer.

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