Water level

To cuboid-shaped poll, bottom size 2m and 3.5m, flows water at a rate of 50 liters per minute.
How long will it take for water to reach a level of 50 cm?

Correct answer:

t =  70 min

Step-by-step explanation:

$$\begin{gathered} a=2\cdot 10=20\text{dm} \\ b=3.5\cdot 10=35\text{dm} \\ c=50/10=5\text{dm} \\ V=a\cdot b\cdot c=20\cdot 35\cdot 5=3500{\text{dm}}^3 \\ v=50{\text{dm}}^3\text{/s} \\ t=V/v=3500/50=70\text{min} \end{gathered}$$

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