To make 200ml of a 20% solution using stock solutions of 10% and 40%, how much of each is needed?

To determine the amounts of 10% and 40% solutions required to create 200 ml of a 20% solution, we can apply the concept of the dilution equation or use the method of alligation. The objective is to mix the two stock solutions to achieve the target concentration.

1. Understanding concentration: The 20% solution means that in 200 ml, we need 40 ml of pure drug (since 20% of 200 ml is 40 ml).

2. Setting up the equation: Let's denote the volume of the 40% solution needed as "x" ml and the volume of the 10% solution as "y" ml. The entire mixture must total 200 ml, so we have:

• x + y = 200 [Equation 1]

3. Amount of drug from each solution: The amount of pure drug contributed by each solution is:

• From the 40% solution: 0.40x ml of the drug

• From the 10% solution: 0.10y ml of the drug

All must equal the total drug needed for the 20% solution:

• 0.40x +