How much pure acid should be mixed with 6 gallons of a 50% acid solution in order to get a 70% acid solution?

To help with thinking about this, we can say that the 6 gallons of 50% acid contains 3 gallons of pure acid and 3 gallons of filler. This would make the concentration 3/6, or 50%. Adding a gallon of pure acid would shift the concentration to 4/7, or 57.1%.

When the relationship becomes 70%, four gallons of pure acid have been added.

3+4 7
—— = — = 70%
6+4 10

i think there was a typo. you wrote pat brings 3 quarts of ice-cream to the party. each serving of ice-cream is 1 6 quart. how many total servings of ice-cream does pat bring to the party? i think the bold is supposed to be 1/6. so 1 quart of ice cream = 6 servings. 6 * 3 = 18.

the answer is 18.