Calculate how much 10% acid solution and how much pure acid must be mixed to end up with exactly 12 liters of 30% acid solution. Rounding to the nearest hundredth of a liter, you'll need ___ liters of the pure acid.

  2.67 liters

Step-by-step explanation:

Let "a" represent the number of liters of pure acid needed to make the desired solution. Then the amount of acid in the mix is ...

  (100%)x +(10%)(12 -x) = (30%)(12)

  (90%)x = 12(20%) . . . . . subtract (10%)(12)

  x = 12(2/9) . . . . . divide by 90%

  x = 2 2/3 . . . liters

You'll need 2.67 liters of the pure acid.