A chemist has 400 grams of salt solution that is 10% salt. How many grams of 20% salt solution must be added to obtain a 12% solution of salt?
You need to add 100 g of the 20% salt solution.
Start by calculating how much salt you get in the 400-g sample of the 10% solution.
Now, let's say that the mass of the 20% solution needed is equal to
The taol mass of the salt in the target 12% solution will be
The total mass of the target solution will be
This means that you can write
Rearrange and solve this equation for
This means that if you add 100 g of the 20% solution to 400g of the 10% solution, you will get 500 g of a 12% salt solution.