3.56 Two pipes of different cross-sections are connected to a swimming pool, one uniformly supplying water, the other uniformly draining it, with the first pipe filling the pool 2 hours longer than the second pipe takes to empty it. When the pool was filled to $\frac{1}{3}$ of its capacity, both pipes were opened, and the pool was found to be empty after 8 hours. How many hours does it take for the first pipe to fill the pool and for the second pipe to empty it when acting separately?

## Mixtures, Alloys

A certain alloy consists of two metals in the ratio $1: 2$, while another contains the same metals in the ratio 2:3. How many parts of each alloy are needed to obtain a third alloy containing the same metals in the ratio 17:27?

A container with a capacity of 8 liters is filled with a mixture of oxygen and nitrogen, with oxygen accounting for $16 \%$ of the container's capacity. A certain amount of the mixture is released from this container and an equal amount of nitrogen is added, after which the same amount of the mixture is released again and the same amount of nitrogen is added. In the new mixture, the oxygen content is $9 \%$. What amount of the mixture was released from the container each time?
3.56 Let's write down the values of the required and given quantities in the form of a table:

| Pipe | Time, h | Capacity | Productivity |
| :---: | :---: | :---: | :---: |
| Supply | $x$ | 1 | $\frac{1}{x}$ |
| Discharge | $x+2$ | 1 | $\frac{1}{x+2}$ |
| Both together | 8 | 1 | $\frac{1}{24}$ |

According to the condition, $\frac{1}{x}-\frac{1}{x+2}=\frac{1}{24}$, from which $x=6$.

Answer: $\quad$ in 6 and 8 h.