Discussion
A closed wooden box has internal dimensions 80 cm long, 48 cm wide and 20 cm deep, and the wood is 4 cm thick. What volume of wood is used in constructing the box?
Answer: B
The wood occupies the space between the outer box and the hollow inside it, so find both volumes and subtract.
The wood is 4 cm thick on every face, so each external dimension exceeds the internal one by \( 2 \times 4 = 8 \) cm:
\[ 88 \times 56 \times 28 \text{ cm} \]
\[ V_{\text{external}} = 88 \times 56 \times 28 = 137{,}984 \text{ cm}^{3} \]
\[ V_{\text{internal}} = 80 \times 48 \times 20 = 76{,}800 \text{ cm}^{3} \]
\[ V_{\text{wood}} = 137{,}984 - 76{,}800 = 61{,}184 \text{ cm}^{3} \]
Adding 4 cm rather than 8 cm to each dimension is the standard error - the thickness is present on both opposite faces.
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