Empty aquarium

How much does an empty aquarium weigh with dimensions: length = 40 cm, width = 30 cm, height = 20 cm, if 1 dm² of glass weighs 300 g? Calculate its weight in kilograms.

Correct answer:

m =  12 kg

Step-by-step explanation:

$$\begin{gathered} a=40\text{cm}\to \text{dm}=40:10\text{dm}=4\text{dm} \\ b=30\text{cm}\to \text{dm}=30:10\text{dm}=3\text{dm} \\ c=20\text{cm}\to \text{dm}=20:10\text{dm}=2\text{dm} \\ \rho =300{\text{g/dm}}^2 \\ S=a\cdot b+2\cdot (a+b)\cdot c=4\cdot 3+2\cdot (4+3)\cdot 2=40{\text{dm}}^2 \\ {m}_1=S\cdot \rho =40\cdot 300=12000\text{g} \\ m=m_1\to \text{kg}=m_1:1000\text{kg}=12000:1000\text{kg}=12\text{kg}=12\text{kg} \end{gathered}$$

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