Problem 5. A reservoir that collects 2000 liters of water is filled by two pipes in 20 minutes. How many liters of water flow per minute from each pipe, if it is known that in one minute 10 liters more water flow from one pipe than from the other?
Solution. First method. If the first pipe fills x liters per minute, then the second pipe fills $x+10$ liters per minute. They fill the reservoir, which holds 2000 liters, in 20 minutes, so

$$
\begin{aligned}
& 20(x+(x+10))=2000 \\
& 20(2 x+10)=2000 \\
& 2 x+10=100 \\
& x=45
\end{aligned}
$$

Thus, the first pipe delivers 45 liters per minute, and the second pipe delivers $45+10=55$ liters per minute.

Second method. In 1 minute, the pipes fill 2000:20=100 liters of water into the reservoir. If the same amount of water flows from both pipes as from the pipe that fills less, then in one minute they would fill $100-10=90$ liters of water. This means that through the pipe that fills less, $90:2=45$ liters of water flow per minute. Finally, through the other pipe, $45+10=55$ liters of water flow per minute.

## VI section