How many liters of a 15% NaCl solution should be mixed with 2 L of a 20% NaCl solution to obtain a 16% NaCl solution?

8 liters of 15% NaCl solution should be mixed with 2 L of a 20% NaCl solution to obtain a 16%  NaCl solution

Explanation:

The method employed here is known as alligation technique.

Alligation is a method used to calculate the proportion of any two solutions to be mixed to prepare final solution of required concentration.

Let the number of liters of the 15% NaCl solution be X

A mixture of X liters of 15% NaCl + 2 liters of 20% NaCl gives X + 2 liters of a solution whose concentration is 16%

X  * 15% + 2 * 20% = 16% * X + 2

0.15X + 2 * 0.2 = 0.16 X + 0.16 * 2

0.15X + 0.4 = 0.16X + 0.32

0.16X - 0.15X = 0.4 - 0.32

0.01X = 0.08

X = 0.08/0.01

X = 8 liters

Therefore, 8 liters of 15% NaCl solution should be mixed with 2 L of a 20% NaCl solution to obtain a 16%  NaCl solution