2022 · Q91
A closed box is built of wood of uniform thickness. Its external dimensions are 12 cm, 10 cm and 8 cm. If the inner surface area is 376 square cm, then what is the thickness of the wood?
Elementary MathematicsMensuration
- A0.5 cm
- B1 cm
- C1.5 cm
- D2 cm
Explanation
Trying thickness 1 cm: inner dimensions 10×8×6 give surface 2(80+48+60) = 376 sq cm, as required. Inner dimensions are (12−2t), (10−2t), (8−2t); setting the inner surface area to 376 gives a quadratic whose valid root is t = 1. The keyed option is B.