Hi, 

Let x represent amount of pure acid(this will be an 100% solution) (90L-x the 10% solution

Write as we Read***

.10(90L-x) + 1.00x = .75*90L

solving for x

.90x = .65*90L

x = 65L, the amount of pure acid. 

(90-65L)=25L   the amount of the 10% solution

checking our answer

2.5 + 65 = 67.5 

Answer by josmiceli(19441)   (Show Source): You can put this solution on YOUR website!
 Let  = liters of pure acid to be added

Let  = liters of 10% acid solution to be added

given:

(1) 

(2) 

----------------------

From (2):

(2) 

(2) 

Subtract (1) from (2)

(2) 

(1) 





And, since

 





65 liters of pure acid and 25 liters of 10% solution are needed

check answer:

 









OK 

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