A biologist has two brine solutions, one containing 4% salt and another containing 16% salt. How many milliliters of each solution should she mix to obtain 1 L of a solution that contains 11.2% salt?

400 mL of 4% salt solution and 600 mL of 16% salt solution need to be mixed

Explanation:

Let's assume concentration of brine salt solutions are in %(w/v) unit.

Final mixture has a concentration of 11.2% salt and volume of 1 L or 1000 mL

Hence, amount of salt in final mixture =

Suppose x mL of 4% salt solution and (1000-x) mL of 16% salt solution need to be mixed to get final mixture

So, amount of salt in x mL of 4% salt solution =

      amount of salt in x mL of 16% salt solution =

Hence,

or,

So, 400 mL of 4% salt solution and 600 mL of 16% salt solution need to be mixed