Water in aquarium

The aquarium cuboid shape with a length of 25 cm and a width of 30 cm is 9 liters of water. Calculate the areas which are wetted with water.

Correct answer:

S =  20.7 dm²

Step-by-step explanation:

$$\begin{gathered} a=25\text{cm}\to \text{dm}=25:10\text{dm}=2.5\text{dm} \\ b=30\text{cm}\to \text{dm}=30:10\text{dm}=3\text{dm} \\ V=9\text{l} \\ {S}_1=a\cdot b=2.5\cdot 3=\frac{15}{2}=7.5{\text{dm}}^2 \\ c=V/S_1=9/7.5=\frac{6}{5}=1.2\text{dm} \\ S=S_1+2\cdot c\cdot (a+b)=7.5+2\cdot 1.2\cdot (2.5+3)=20.7{\text{dm}}^2 \end{gathered}$$

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