How many ounces of a 7 acid solution and how many ounces of
     How many ounces of a 7% acid solution and how many ounces of a 23% acid solution must be mixed to obtain 20 oz of a 17% acid solution? 
  
  Solution
x ounces of 7% acid solution
y ounces of 23% acid solution
x + y = 20
7% of x + 23% of y = 17% of 20
0.07*x + 0.23y = 0.17*20 = 3.4
Solving both equations:
x = 7.5 ounce
y = 12.5 ounce

