A solution of salt weighing 150 g with a concentration of 40% was mixed with 450

A solution of salt weighing 150 g with a concentration of 40% was mixed with 450 g of pure water. What is the concentration of the resulting mixture?

Salt solution weighing 150 gr. has a concentration of 40%, which means that the salt in this solution contains:
150 * (40% / 100%) = 150 * 0.4 = 60 (g) salt

The solution had a mass of 150 g. and another 450 g was added to it. water, then the mass of the solution has become:
150 + 450 = 600 (g) the mass of the new solution

The new solution weighs 600 grams and contains 60 grams. salt, then its concentration is equal to:
(60/600) * 100% = 0.1 * 100% = 10%

Answer: 10%.