Question 1146352
x = the number of liters of the 20% solution.
y = the number of liters of the 60% solution.


you want 25 liters of a 28% solution.
that would require .28 * 25 = 7 liters of acid.


you have two equatons that need to be solved simultaneously.
they are:


x + y = 25
.2x + .6y = 7


multiply both sides of the first equation by .2 and leave the second equation as is to get:


.2x + .2y = 5
.2x + .6y = 7


subtract the first equation from the second to get:


.4y = 2


solve for y to get y = 5


since x + y = 25, then x = 20


your solution is that you need 20 liters of the 20% solution plus 5 liters of the 60% solution to get 25 liters of the 28% solution.


.2 * 20 + .6 * 5 = 7


7/25 = .28 = 28%