Was evaporated to dryness 600 grams of sodium hydroxide concentration of 20%

Was evaporated to dryness 600 grams of sodium hydroxide concentration of 20% was added 80 grams of water. What is the concentration of the solution?

Given:
m1 solution (NaOH) = 600 g
ω1 (NaOH) = 20%
m (H2O) = 80 g

Find:
ω2 (NaOH) -?

Solution:
1) m (NaOH) = ω1 (NaOH) * m1 solution (NaOH) / 100% = 20% * 600/100% = 120 g;
2) m2 solution (NaOH) = m (NaOH) + m (H2O) = 120 + 80 = 200 g;
3) ω2 (NaOH) = m (NaOH) * 100% / m2 solution (NaOH) = 120 * 100% / 200 = 60%.

Answer: The mass fraction of NaOH is 60%.