how many liters of a 12% salt solution must be added to 10 liters of a 25% salt solution to get a 20% salt solution?

There must be added 6.25L of a 12% salt solution

Step-by-step explanation:

We add 'x' litres of 12% salt solution into 10 litres of 25% salt solution, so resulting in "x+10" litres of 20% salt solution.

x litres of 12% salt solution + 10 litres 25% salt solution = (x+10) litres 20% salt solution

this gives us the formula:

x (12) + 10 (25) = (x+10) 20

12x + 250 = 20x + 200

-8x = - 50

x=6.25

Therefore add 6.25 litres of 12% salt solution to 10 litres of 25% salt solution to obtain a 20% salt solution.