Question 272694
A solution of 9% is mixed with a solution of 30% to form an 18% solution.  How many of each solution should be used to form 21 liters of the 18% solution?


Let 30% solution added be x

9%------------------ 30%------------------ 18% mix

21-x---------------------x-----------------------21

0.09(21-x)+0.3x= 0.18*21

1.89-0.09x+0.3x = 3.78

1.89 + 0.21x =3.78

0.21x= 3.78-1.89

x= 1.89/0.21

x= 9 liters  = 30 % solution

21-9 = 12 liters 9% solution