13.253. For hydrodynamic studies, a small model of a channel has been made. Several pipes of the same cross-section, supplying water, and several pipes of another, but also the same cross-section, intended for removing water, are connected to this model. If four inlet and three outlet pipes are opened simultaneously, then after 5 hours, the volume of water in the model will increase by 1000 m ${}^{3}$. If two inlet and two outlet pipes are opened simultaneously for 2 hours, the increase in the volume of water will be $180 \mathrm{~m}^{3}$. How much water does one inlet pipe and one outlet pipe pass in one hour?
## Solution.

Let $x$ m $^{3} /$ h be the flow rate of the inlet pipe, and $y$ m $^{3} /$ h be the flow rate of the outlet pipe. According to the problem,
$\left\{\begin{array}{l}5(4 x-3 y)=1000, \\ 2(2 x-2 y)=180,\end{array}\right.$

from which $x=65 \mathrm{~m}^{3}, y=20 \mathrm{~m}^{3}$.

Answer: 65 and $20 \mathrm{~m}^{3}$.