Second Type of Question
Calculating the Amounts of Solutions/Mixtures Needed
As said, you may need to prepare a solution (or mixture) of a specified strength from two or more solutions of known strength. You must be able to calculate how much of each solution you need.
You need to prepare 100g of a powder containing 8% Zinc Oxide. You have 2 powders available; the first contains 10% Zinc Oxide; the second contains 5% Zinc Oxide. How much of each Powder do you need?
Again, you are, in a way, considering weighted averages. For example. You have two powders: the first has a high concentration, the second has a low concentration. As the strength of the required powder increases, you should be able to see that you will need more of the high concentration powder: the proportion of the high concentration powder needed increases.
Alligation allows you to find the proportions of the powders that you need to mix together to achieve the required concentration.