Water tank

The block-shaped tank is 2.5 m long, 100 cm wide, and 12 dm high. Water flows into the tank at 40 liters per minute. In how many minutes will it be filled with water to two-thirds?

Correct answer:

t =  50 min

Step-by-step explanation:

$$\begin{gathered} a=2.5\text{m} \\ b=100\text{cm}\to \text{m}=100:100\text{m}=1\text{m} \\ c=12\text{dm}\to \text{m}=12:10\text{m}=1.2\text{m} \\ {V}_1=a\cdot b\cdot c=2.5\cdot 1\cdot 1.2=3{\text{m}}^3 \\ {V}_2=\frac{2}{3}\cdot V_1=\frac{2}{3}\cdot 3=\frac{2\cdot 3}{3}=\frac{6}{3}=2{\text{m}}^3 \\ Q=40\text{l/min} \\ {V}_3=V_2\to \text{l}=V_2\cdot 1000\text{l}=2\cdot 1000\text{l}=2000\text{l} \\ t=V_3/Q=2000/40=50\text{min} \end{gathered}$$

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