How many square pieces of cardboard of side 40 cm are required to make a box of dimensions 80 cm × 40 cm × 20 cm?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 7
The cardboard must cover all six faces of the box, so the area needed is the total surface area of the cuboid, \(2(lb+bh+lh)\); dividing it by the area of one square piece gives the number of pieces.
Total surface area \(=2(80\times40+40\times20+80\times20)=2(3200+800+1600)=11200\,\mathrm{cm^2}\)
Area of one piece \(=40\times40=1600\,\mathrm{cm^2}\)
Number of pieces \(\displaystyle =\frac{11200}{1600}=7\)