Multiple choice

John wants to make a $100$ ml of $5\%$ alcohol solution mixing a quantity of a $2\%$ alcohol solution with a $7\%$ alcohol solution. What is the quantity of $2\%$ he should use.

  1. $60$ ml
  2. $80$ ml
  3. $40$ ml
  4. $50$ ml
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A Correct answer
AI explanation

Using the rule of alligation, the ratio of the 7% solution to the 2% solution is (5 - 2) : (7 - 5), which equals 3 : 2. Let the quantity of the 2% solution be x, so the quantity of the 7% solution is (100 - x). Then x divided by (100 - x) equals 3 divided by 2, which yields 2x = 300 - 3x and x = 60. The required quantity of the 2% solution is 60 ml.

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