Question

how much of a brand A fruit punch (35% fruit juice) must be mixed with 9L of grape juice to create a mixture containing 74% fruit juice?

Answer 1

Grape juice is 100% fruit juice so for 9 liters of grape juice you have 9 liters of fruit juice

9 liters fruit juice    
9 liters juice

for every liter you add of fruit punch, you get .35 liters of fruit juice. so the question is how many liters of punch (we'll say x liters) do you have to add to get the ratio of fruit juice to total juice to be 74 to 100?

9 liters of fruit juice + 0.35x          =           74     
      9 liters of juice + x                             100

cross multiply

(9 + 0.35x) 100 = (9 + x)74
900 + 35x = 666+ 74x
234 = 39x
x=6 liters of brand A fruit punch