Final answer:
To find the volumes of 3% acid solution and 7% acid solution needed to yield 120 mL of 5% acid solution, set up a system of equations. Solve the system to find the volumes.
Step-by-step explanation:
To find the number of milliliters of 3% acid solution and 7% acid solution needed to yield 120 mL of 5% acid solution, we can set up a system of equations. Let x represent the volume of the 3% acid solution and y represent the volume of the 7% acid solution. The total volume of the final solution is 120 mL, so we have the equation x + y = 120.
The concentration of acid in the final solution is 5%, so we can also set up the equation (0.03x + 0.07y)/(x + y) = 0.05. Solving this system of equations will give us the values of x and y, which represent the volumes of the 3% and 7% acid solutions, respectively.