3. From a vessel containing 5 liters of a $6 \%$ acid solution, 1 liter was poured out, after which 2 liters of water were added. Find the concentration of the resulting solution.
Solution. After pouring out 1 liter, 4 liters of the solution remained in the container, with the amount of acid being $4 \cdot 0.06 = 0.24$ liters. After adding two liters of water, the volume of the solution became 6 liters, while the amount of acid remained unchanged. Thus, the concentration of the acid became $0.24 : 6 = 0.04$.

Answer: 0.04.