Cardboard

How many m² of cardboard are needed to make the cuboid with dimensions 40 cm 60 cm and 20 cm?

Correct answer:

x =  0.88 m²

Step-by-step explanation:

$$\begin{gathered} a=40\mathrm{/}100={\displaystyle \frac{2}{5}}=0.4\text{ m } \\ b=60\mathrm{/}100={\displaystyle \frac{3}{5}}=0.6\text{ m } \\ c=20\mathrm{/}100={\displaystyle \frac{1}{5}}=0.2\text{ m } \\ x=2\cdot (a\cdot b+b\cdot c+a\cdot c)=2\cdot (0.4\cdot 0.6+0.6\cdot 0.2+0.4\cdot 0.2)={\displaystyle \frac{22}{25}}={\displaystyle \frac{22}{25}}{\text{m}}^2=0.88{\text{m}}^2 \end{gathered}$$

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