George wishes to increase the percent of acid in 50ml of a 15% acid solution to 25% acid, how much pure acid must he add?

Let's use the decimal equivalent of percent. He has 50 ml of a 0.15 acid solution. He wants the concentration of acid to increase to 0.25 by adding pure acid.

concentration = (volume of acid)/(total volume of solution)

He takes the current solution and add x amount of pure acid.

15% of 50 ml = 7.5 ml

The current 15% solution contains 7.5 ml of pure acid. The x amount of acid he adds is added onto the 7.5 ml of acid he already has and it is also added to the total volume of 50 ml.

(7.5 + x)/(50 + x) = 0.25

7.5 + x = 0.25(50 + x)

7.5 + x = 12.5 + 0.25x

0.75x = 5

x = 6.6666...

6 2/3 ml

they used 313 gallons of paint