Let x represent the number of liters of 50% acid Theresa puts into the mix. The the number of liters of 30% acid will be (420-x). The total amount of acid in the final solution will be ...
  0.50x + 0.30(420-x) = 0.45(420)
  0.20x + 126 = 189 . . . . . . . . . . . . . . . simplify
  0.20x = 63 . . . . . . . . . . . . . . . . . . . . . subtract 126
  x = 63/0.20 = 315 . . . . . . . . . . . . . . . liters of 50% solution
  (420-x) = 420-315 = 105 . . . . . . . . . liters of 30% solution
Theresa should mix ...
   105 liters of 30% solution
  315 liters of 50% solution
        
             
        
        
        
The fraction between 1/2 and 2/2 is 1/4
        
             
        
        
        
7+5(p-p)=7 
because 7+5p-5p=7
cross our the 5p because 5p-5p is 0
7=7
~JZ
Hope it helps!
        
             
        
        
        
6 pints.
2 pints in a quart
        
                    
             
        
        
        
The answer to this is C. (28,10) and (22,2).