An 18% salt solution weighing 2 kg was mixed with one glass of water (0.25 kg). Find the percentage of the resulting solution.

To solve our problem, it is most convenient to use the proportion, so we will compose it. Knowing that the 18% solution has a mass of 2 kg, we can write that:

18% – 2 kg,

Then, after adding 0.25 kg of water to the solution, it will weigh: 2 kg + 0.25 kg. But we do not know its percentage (and, in fact, we need to find it). Now we can make a full proportion:

18% – 2 kg

x% – 2 kg + 0.25 kg,

Multiplying the “crosswise” proportion, we get the answer:

2 * x = 18 * (2 + 0.25);

2x = 36 + 4.5;

2x = 40.5;

x = 40.5: 2 = 20.25 (%).

So now the percentage of the solution is 20.25%.