A chemist mixes a 40% acid solution and a 30% acid solution. How many liters of the 40%
solution must be added to produce 50 liters
of a solution that is 36% acid?

x = liters of 40% solution, which contributes a total of 0.4x liters of acid

y = liters of 30% solution, which contributes a total of 0.3y liters of acid

The chemist wants to end up with 50 liters, so

x + y = 50

and 36% of this -- 0.36 (50 liters) = 18 liters -- is acid, so that

0.4x + 0.3y = 18

Solve for x and y :

y = 50 - x

0.4x + 0.3 (50 - x) = 18

0.4x + 15 - 0.3x = 18

0.1x = 3

x = 30

y = 20

foucusing is the hope this works for you (: