We need to mix 30 liters of the 10% salt solution.
Work Step by Step
Let X represent the amount of the 10% salt solution that is to be mixed. The second solution is 15 liters. That means that the final solution will be 15 + X = 15 + X liters. We use the following guideline to solve this problem: Amount of salt in the first solution + Amount of salt in the second solution = Amount of salt in final solution. 10% $\times$ X +40% $\times$ 15= 20% $\times$ (15 + X) $ .1 \times X + .4\times 15 = .2 \times (15+X)$ 0.1X + 6 = 3 + 0.2X 3 = 0.1X Divide both sides by 0.1 30 = X We need to mix 30 liters of the 10% salt solution.