Two containers of 10 liters each with saline solutions of 10% and 15% concentration are given.

Two containers of 10 liters each with saline solutions of 10% and 15% concentration are given. There are also three more empty containers 3L, 4L, 5L. How to get 1 liter of 12% solution using transfusions?

By condition, we are given two solutions, the first solution is ten liters with ten percent solutions, the second with fifteen percent solution. We are also given three containers: three, four and five liter.
In order to get a twelve percent solution, we must pour three liters of the first solution (10%) and two liters of the second solution (15%) and as a result we get (0.1 * 3 + 0.15 * 2) / 5 we get 0, 12, that is, a twelve percent solution of five liters. Then we pour it into a four liter container and we have one liter of a 12% solution in a five liter container