Step 1 :Let's denote the amount of the 40% solution as x and the amount of the 60% solution as y.
Step 2 :We can set up two equations based on the information given. The first equation is based on the total volume of the solution, which is 120L. This gives us: \(x + y = 120\)
Step 3 :The second equation is based on the total amount of dye in the solution. The amount of dye in the 40% solution is 0.4x, and the amount of dye in the 60% solution is 0.6y. The total amount of dye in the 120L solution is 50% of 120L, or 60L. This gives us: \(0.4x + 0.6y = 60\)
Step 4 :We can solve this system of equations to find the values of x and y. The solution to the system of equations is x = 60 and y = 60.
Step 5 :This means that we need 60L of the 40% solution and 60L of the 60% solution to get 120L of a 50% solution. This makes sense because the final solution is exactly in the middle of the two initial solutions in terms of dye concentration, so we need equal amounts of each.
Step 6 :Final Answer: We need \(\boxed{60}\) liters of the 40% solution and \(\boxed{60}\) liters of the 60% solution.