by adding distilled water to a 15% acid solution, the acid becomes more diluted and percentage of acid is lowered. we can use the following formula c1v1 = c2v2 where c1 is concentration in percentage form and v1 is volume of the concentrated solution c2 is concentration and v2 is volume of the diluted solution substituting these values in the formula 15% x 20 L = C x 30 L C = 10% concentration of acid in new solution is 10%
