Multiple choice

Directions: Answer the question independently. A scientist has a large supply of pure acid and water. He is equipped with two vessels, one of capacity 100 gallons and one of capacity 10 gallons, and with these he desires to attain a certain concentration of acid. He starts with 100 gallons of pure acid. He draws 10 gallons and replaces it with water. Then he draws 10 gallons of the mixture and replaces it with acid. Again he draws 10 gallons and replaces it with water, and finally he draws 10 gallons and replaces it with acid. What is the final concentration of acid?

  1. 65.6%

  2. 82.8%

  3. 85.7%

  4. 83.71%
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Initial: 100% acid. 1: Draw 10, add 10 water (90% acid). 2: Draw 10 (9% acid removed), add 10 acid (90% - 9% + 10% = 91% acid). 3: Draw 10 (9.1% acid removed), add 10 water (91% - 9.1% = 81.9% acid). 4: Draw 10 (8.19% acid removed), add 10 acid (81.9% - 8.19% + 10% = 83.71% acid).

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