120 grams of water was added to 620 grams of a 40% salt solution, then 40 grams of water

120 grams of water was added to 620 grams of a 40% salt solution, then 40 grams of water was evaporated, determine the concentration of the resulting solution.

Explanation: to solve this problem, you need to use the following formula:
w = m (solv.v-va) / m (solution), where w is the mass fraction of the dissolved substance in the solution, m (solv.v-va) is the mass of sol. in-va, m (solution) is the mass of the solution.
Find the mass of sol. salt substances:
m (solution in-va) = w * m (solution) = 0.4 * 620 = 248 g.
We substitute the values into the formula and we get (considering that 40 g of water was evaporated from the mass of the solution):
w = m (solution in-va) / m (solution) = 248/620 + 120-40 = 0.3543.