5 grams were added to 40 grams of a 10% salt solution and 25 ml of water was poured. What is the mass fraction of salt in this solution

Decision:
For calculations we will use the equation:
w% = [m (salt). 100%] / m (p-pa).
Calculate the mass of salt contained in a 10% solution of it, we get:
m (salt) = [w%. m (p-pa)] / 100% = (10. 40) / 100% = 4 g.
Determine the total mass of salt, we get:
mtotal (salt) = m (salt) + 5 = 4 + 5 = 9 g.
Calculate the total mass of the solution, we get:
total (p-pa) = 40 g + 25 g = 65 g.
We find the mass fraction of salt in this solution, we get:
w% = (9. 100) / 65 = 13.85%.
Answer: w% = 13.85%.