Multiple choice

The quantity of water that should be added to reduce 18 ml lotion containing 50\% alcohol to a lotion containing 30\% alcohol is-

  1. 6 ml

  2. 8 ml

  3. 10 ml

  4. 12 ml
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Initial alcohol = 50% of 18 ml = 9 ml. Let x ml water be added. Total volume = (18+x) ml, alcohol = 9 ml. For 30% concentration: 9/(18+x) = 0.3, so 9 = 0.3(18+x), giving 9 = 5.4 + 0.3x, therefore x = 3.6/0.3 = 12 ml. Option A (6 ml) might result from incorrectly solving 9/(18+x) = 0.5.

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