Verified answer

Let,

pure acod added = x pints

SO,

(33+x)*25/100 = 3+x,

OR,

33*25 + 25x = 300 +100x,

OR,

25x -100x = 300 -33*25 = 300 - 825,

OR,

-75x = -525,

OR,

x = 525/75 = 7 pints >============================< ANSWER

Percent of pure acid in original solution:

3 pints/33 pints = 0.09 = 9%

25% = 0.25

x = total number of pints of acid for a 25% solution

x/33 = 0.25

x = 0.25(33)

x = 8.25 total number of pints of acid for a 25% solution

8.25 - 3.00 = 5.25 number of pints added for a 25% solution

3+x = 0.25(x+33)

3+x = 0.25x+8.25

0.75x = 5.25

x = 7 pints of pure acid