Mixed 2 solutions: 200g salt, 20% solution and 150g – 35% solution. Determine the mass fraction of salt in the new solution.

The mass fraction of salt can be calculated as the ratio of its mass to the mass of the solution.
The mass of salt in the new solution is the sum of its masses in the two previous solutions:
200 * 0.2 + 150 * 0.35 = 92.5 grams
The mass of the new solution is the sum of the masses of the two previous solutions:
200 + 150 = 350 grams
Mass fraction of salt in the new solution:
92.5 / 350 = 0.264
As a percentage, this is 0.264 * 100% = 26.4%